Appendix D CEE (2018) Seawater and Wastewater Treatment and Solids Handling Facilities Options Study and Concept Design

Transcription

1 Yumbah Nyamat Works Approval Application October 2018 Appendix D CEE (2018) Seawater and Wastewater Treatment and Solids Handling Facilities Options Study and Concept Design

2 Yumbah Nyamat Abalone Farm Lots 1 and 8, 215 Dutton Way, Portland Seawater and Wastewater Treatment and Solids Handling Facilities Options Study and Concept Design October 2018

3 Yumbah Nyamat Abalone Farm Lots 1 and 8, 215 Dutton Way, Portland Seawater and Wastewater Treatment and Solids Handling Facilities Options Study and Concept Design Prepared for: Yumbah Aquaculture 68 Snapper Point Road Allestree VIC 3305 Prepared for: CEE Pty Ltd Environmental Engineers and Scientists Unit 4, 150 Chesterville Road, Cheltenham VIC 3192 Tel: Contact: John Anderson Mob: anderson@cee.com.au Document History and Status Revision Date Description Prepared By Approved By Comment Oct 18 Final to Client J. Anderson T Rudge For EPA WAA Document Limitations This document has been prepared in accordance with an agreement between CEE and the Organisation to whom this report is addressed. The services performed by CEE have been conducted in a manner consistent with the level of quality and skill generally exercised by members of its profession and consulting practices. This report is prepared solely for the use of the person or organisation for which this report is addressed and in accordance with the terms of engagement for the commission. Any reliance of this report by third parties shall be at such party s sole risk. The report may not contain sufficient information for the purposes of other parties or for other uses. This report shall only be presented in full and shall not be used to support any other objectives than those set out in the report, except where written approval is provided by CEE. October 2018 Page i

4 Table of Contents 1 Introduction Background Study and Wastewater Treatment Objectives Scope of Work Conduct of study Acknowledgments 3 2 Proposed Yumbah Nyamat Abalone Farm and Operation Outline of Facilities Description of Wastewater Collection and Conveying Facilities and Operation Inlet pipework and pump station Abalone tanks Internal Lateral Drains from abalone tanks Southern Collection Channel 6 3 Seawater and Wastewater Flows, Characteristics and Loadings Seawater Flow Characteristics Particle size distribution Inlet sand loads Wastewater flow Characteristics and loads Abalone Feed Abalone faeces Treated Wastewater (based on Yumbah Narrawong) Estimated loads based on testing on 19 July Mass balance summary 16 4 Wastewater Management Issues Variation in wastewater flow Variation in solids load Variation in sand concentration in seawater pumped to farm Diurnal variation in abalone tank discharge characteristics Solids settling rates Sand 20 October 2018 Page i

5 4.3.2 Food pellets Faeces Solids Settling in Southern Collection Channel Solids Solubilisation Solids degradation Salt in dewatered sludge requiring disposal Other issues 24 5 Wastewater Treatment and Solids Handling Options Objectives Potential Options Do Nothing option Assessment Solids Settling Ponds (SSPs)(as per Yumbah Narrawong) Description Operation Assessment Solids Settlement Tanks (as per SECs at Yumbah Narrawong) Description Operation Assessment Solids Settling Channels Description Operation Assessment Vortex-type Solids Settling Tanks Description Operation Assessment Screens and filters Description Operation Assessment Basket screen option Description Operation Assessment Other options Cyclones 35 October 2018 Page ii

6 5.9.2 Solids dewatering Cleaning of abalone tanks Cleaning of Southern Collection Channel and/or Solids Settling Channels Assessment of options 36 6 Concept Design of Wastewater Treatment System Description Operation 39 7 Appendix A References 41 8 Appendix B Mass Balances Yumbah Nyamat Mass balance based on Existing Yumbah Narrawong Solids Removal Facilities Yumbah Nyamat Mass balance based on Proposed Solids Settling Channels 44 October 2018 Page iii

7 List of Tables Table 2-1: Wastewater and solids collection and conveyance system design and operation 7 Table 3-1: Ambient seawater quality ( median and 80 th percentiles) at Yumbah Narrawong ( ) 8 Table 3-2: Summary of particle size distribution (microns) for seawater inlet to abalone tanks at Yumbah Narrawong 9 Table 3-3: Ambient seawater quality and solids settling ponds (SSPs) and channel (SEC) outlet characteristics (median and 80 th percentiles) at Yumbah Narrawong ( ) 12 Table 3-4: Summary of estimated flows, SS concentrations and loads for various stages of the farm for morning tipper operation and for daily average (19 July 2018) 16 Table 3-5: Summary of estimated return flows, concentrations and loads (SS, carbon, total N, ammonia and total P) for the average flow and feed case, based on solids removal efficiency achieved at existing Yumbah Narrawong solids settling facilities 17 Table 3-6: Summary of estimated increase in concentrations and loads (SS, carbon, total N, ammonia and total P) through the Yumbah Nyamat farm for the average flow and feed case, based on solids removal efficiency achieved at existing Yumbah Narrawong treatment facilities 17 Table 4-1: Summary of wastewater flows 18 Table 4-2: Summary of ambient seawater characteristics 19 Table 4-3: Summary of wastewater discharge characteristics during the morning tank cleaning (tipper) operation and during the afternoon (i.e. no tank cleaning) on 19 July Table 4-4: Calculated settling velocities (cm/s) in seawater for sand with SG of 2.4 for different sand particle sizes using Newton s Law and different shape factors 21 Table 4-5: 50 th percentile performance of Yumbah Narrawong solids settling ponds/tank (2001 to 2018) 23 Table 4-6: Summary of estimated annual solids loads for various solids removal efficiencies 24 Table 5-1: Assessment of solids removal options 37 Table 6-1: Solids Settling Channel details 40 October 2018 Page iv

8 List of Figures Figure 3-1: Particle size distribution for seawater discharged to the existing abalone tanks at Yumbah Narrawong (24 August 2017) 9 Figure 3-2: Total nitrogen concentration in the discharge from the solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) 13 Figure 3-3: Ammonia concentration in the discharge from the solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) 13 Figure 3-4: Typical particle size distributions for ambient seawater and wastewater discharged to the existing solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) 14 Figure 3-5: Typical particle size distributions for wastewater discharged from the existing solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) 15 Figure 4-1: Predicted settling rates (cm/s) for sand in freshwater versus particle size (micron). 21 Figure 5-1: Conventional vortex solids settling tank (e.g. Pista Grit) 30 Figure 5-2: Grit King vortex solids settling tank 32 Appendices October 2018 Page v

9 1 Introduction 1.1 Background (Yumbah) has operated an abalone farm at Narrawong (referred as Yumbah Narrawong), near Portland for over 15 years, that produces 220 tonne of abalone annually (t/a). Yumbah propose to establish a 1000 t/a capacity abalone farm nearby on Dutton Way, Portland (referred to as Yumbah Nyamat). The facility will have similar infrastructure to Yumbah Narrawong and will be the largest abalone farm in the southern hemisphere. The Yumbah Nyamat farm will pump seawater from the adjacent coastal waters through a fourmodule land-based abalone farm and discharge the wastewater back to the marine environment through outfall diffuser pipes. A major challenge at Yumbah Nyamat is dealing with the ocean born sand (i.e. >150 micron (um)) that is suspended in the water column adjacent to the inlet pipes. Experience at Yumbah Narrawong shows that this sand, together with feed pellets not eaten by the abalone, settle out the abalone tanks, requiring daily flushing to control solids build-up. The median concentration of this incoming sand is 3.3 mg/l (i.e. 1.5 t/d of sand at average inflow of 5.2 m 3 /s). Sediment build-up also occurs in the upstream supply pipework at Yumbah Narrawong, in the downstream slow flowing drainage system, and in the solids/liquid separation facilities. These are ongoing in-house management issues that require significant manual labour input, involving manually moving the settled solids downstream along the various collection and conveyancing channels on a regular basis.. Based on this Yumbah Narrawong experience, the preferred location to remove the ocean born sand is at the front end of the farm via a series of drop box settlement pipes or similar settlement systems, rather than at the end of the system as practiced at Yumbah Narrawong. The benefits of removing sand at the head of the abalone tanks include: a cleaner more hygienic environment for the abalone removes the need to handle sand in the tanks and in the drainage network. simplifies removal of organics (mainly uneaten feed) from the wastewater discharge. Removing sand at the inlet however, comes at a significant capital cost. Options to remove sand at both upstream and downstream of the system require development and evaluation. The abalone production process generates waste matter (mainly organics and nutrients), consisting primarily of abalone faeces (mainly as dissolved solids) and uneaten feed pellets (settleable solids). These added wastes result in an increase in organic and nutrient (including ammonia) concentrations and load discharged to the marine environment. At Yumbah Narrawong, the wastewater is treated in solids settlement ponds (SSPs) (DP1 andp2) and in a sediment entrainment channel (SEC) (DP3) to remove readily settleable matter prior to October 2018 Page 1

10 discharge to the marine environment. The accumulated solids are periodically removed from the solids settling facilities to landfill. This treatment method and a range of other solids removal options are developed and evaluated in this report. 1.2 Study and Wastewater Treatment Objectives CEE Pty Ltd (Consulting Environmental Engineers and Scientists) was engaged by Yumbah to investigate treatment options to remove ocean born sand and organics from the wastewater prior to the return to the marine environment, and develop the concept design of the preferred treatment and solids handling facilities. The principal objectives of the abalone wastewater treatment and solids handling facilities are: maximise removal of uneaten abalone feed to reduce organic load and nutrient concentrations discharged, and thereby ensuring that the treated wastewater (i.e. return water) meets licence conditions and does not cause environmental harm to the receiving coastal waters separate treatment facilities for wastewater from each module prior to discharge to the marine environment to assist with maximising the biosecurity of the farm use wastewater processes and equipment that meets best wastewater industry practice provides efficient, reliable environmentally friendly and safe operation maximises segregation of wastes and reuse minimises solid waste material generated from the system. 1.3 Scope of Work The scope of work for this assignment involved the following tasks: Undertake site meeting and inspection of the Yumbah Narrawong abalone farm to confirm existing facilities and operations, issues and constraints, and identify options Review preliminary site layout drawings and recent monitoring data Identify additional testing and monitoring to be undertaken Develop and evaluate options to remove ocean born sand and waste organics/nutrients produced and associated solids handling options Describe preferred project works. 1.4 Conduct of study John Anderson (CEE Principal Process Engineer) visited the Yumbah Narrawong and Yumbah Nyamat sites in June 2018 to undertake an inspection of facilities and operations and to discuss issues with Yumbah Narrawong personnel (Tim Rudge and Sarah Smith). CEE then completed a desktop review and assessment culminating in this options and concept design report. October 2018 Page 2

11 1.5 Acknowledgments We wish to record our appreciation of the valuable assistance and willing support provided during this study by Yumbah s Narrawong Abalone Farm staff, particularly that provided by Tim Rudge and Sarah Smith. October 2018 Page 3

12 2 Proposed Yumbah Nyamat Abalone Farm and Operation 2.1 Outline of Facilities Much of the design and operation of the Yumbah Nyamat farm is based on that of the nearby Yumbah Narrawong abalone farm. The major components and features of the Yumbah Nyamat abalone farm are: 1. Seawater inlet pipework and pump station 2. Sand removal facility on inlet pipework (option A) 3. Abalone tanks and associated flushing system 4. Internal Lateral Drains 5. Southern Collector Channel 6. Sand removal facility on discharge (option B), with associated removal of uneaten pellets to remove organics and nutrients 7. Discharge outfall pipelines to the receiving waters. The following subsection describes the proposed facilities and operation of components 1, 2, 4, 5, and 7. Options for components 2 and 6 are developed and evaluated in Section 4 and Description of Wastewater Collection and Conveying Facilities and Operation Inlet pipework and pump station Seawater is pumped continuously from the adjacent marine environment at an average flow of 5.2 m 3 /s to the farm. The inlets to the pipelines are located 400 m offshore at a water depth of approximately 6 m. The suction inlets are located at approximately mid-water depth to minimise suspended matter entering the pipelines. The inlet pipework (i.e. up to the inlet pumps) is pigged quarterly (based on current operation at Yumbah Narrawong) to remove sand and biofouling accumulation. Cleaning of the internal seawater supply pipework (i.e. downstream of the inlet pumps) will be undertaken as required, however at a reduced frequency to that currently undertaken at Yumbah Narrawong (i.e. daily, weather dependant), with the operation of the proposed ocean borne sand removal facility Abalone tanks The farm is divided into 4 modules, each with 500 abalone tanks (i.e. total 2000 tanks). The tanks are 20 m x 2.8 m and have a nominal water depth of 50 mm (2.8 m 3 ). Seawater is pumped October 2018 Page 4

13 continuously into each tank at a constant rate of 2.6 L/s and flows slowly along the length of the tank before discharging into the internal lateral drainage system. Feed, in the form of pellets, is added daily (during the afternoon) to the tanks. The abalone feed on the pellets during the night. Sand and organic matter settle out in the quiescent tank environment, as follows: 1520 kg/d of fine sand suspended in the incoming seawater, with median SS concentration of 3.3 mg/l, and median particle size of 100 micron. 214 kg/d of uneaten abalone feed, based on 5% of total feed of 1560 t/a, consisting of nominal 5-7 mm long pellets Few whole and part abalone shells (up to ~ 60 mm) An average of 1110 kg/d of abalone faeces (2.4 mg/l) is estimated to be produced at Yumbah Nyamat. The faeces are characterised as small, light and fluffy, and most faeces dissolve relatively quickly into the seawater (particularly during tank flushing) (refer Section 3 for basis of estimate). The composition, characteristic and estimated loads at Yumbah Nyamat for sand, pellets and faeces (in terms of suspended solids, organics and nutrients) are presented in Section 3. Most of the sand present in the seawater (i.e. >50 micron), and the uneaten feed pellets settle out in the abalone tanks during the nominal 18-minute hydraulic retention time (i.e. average settling rate of > cm/s). Solids accumulation in the tanks is controlled with regular flushing with seawater from tippers. There are 1000 tippers, with each tipper serving 2 tanks. Thus, only half the tanks are cleaned at a time). The tank flushing process involves filling the 0.75 m 3 capacity tippers at a constant flow of 1 L/s and when full the tipper unloads the contents in to one end of the abalone tank. This operation is repeated up to about 10 times (depending on the season) and takes up to 2.5 hours. Following this flushing of 1000 tanks, the tippers are moved to the second tanks served by the tipper, and the flushing process is repeated on the second set of 1000 tanks. The flushing process is normally undertaken in the morning between 6 am to noon (i.e. nominal 5 hour period prior to feeding). Daily flushing is undertaken during summer and every second day during autumn, winter and spring. The tippers can be located at each end of the tanks, thereby enabling tank flushing in both directions as required Internal Lateral Drains from abalone tanks Forty (40) internal drainage channels receive discharge from each end of the abalone tanks (i.e. 10 drains per module with 5 rows of tanks). Each channel services 100 tanks (one end only) and is 335 m long and 0.6 m wide. The channels slope at 0.5% (1:200) from the north to the Southern Collection Channel (refer Table 2-1). These internal drains are expected to remain relatively clean (based on Yumbah Narrawong farm operating experience), with most solids being transported to the main channel during the October 2018 Page 5

14 morning tipper operation. The drains are expected to be manually swept bi-annually to the main collection channel. There is potential to collect abalone shells and possibly uneaten pellet feed at the discharge end of the. Options include abalone catching baskets and mechanical filters (i.e. drum filters). The number of baskets/filters required can be reduced by combining pairs of drains in close proximity to each other (minimum of six baskets/filters per module). These options are discussed in Section Southern Collection Channel A 2 m wide 500 m long channel receives abalone tank drainage from the 40 internal drains. The channel consists of four 125 m long sections (i.e. one for each module) that are normally isolated from each other with penstocks (for biosecurity reasons). Drainage water discharges from each of these four sections into individual solids removal facilities prior to discharge back into the receiving waters. The channel is flat bottomed with no grade and a depth of 0.75 m at the outlets. The drainage water velocity in the 4 sections increases along the channel up to 0.87 m/s at average flow and up to 1.0 m/s at peak daily flow. Solids accumulation is expected to occur in the Southern Collection Channel, but less than that observed at Yumbah Narrawong (i.e. up to 200 mm thick). The solids consist primarily of fine sand, with most of the lighter organic matter normally being transported downstream. Periodic manual cleaning is required at Yumbah Narrawong using high pressure water jets to move the settled solids downstream into the solids removal facilities. This is labour intensive with high operating/maintenance costs. There are a number of options available to reduce and/or eliminate the need for manual cleaning (refer Section 4). Table 2-1 summarises the design criteria/details and operation/performance for the abalone tanks and drainage system. October 2018 Page 6

15 Table 2-1: Wastewater and solids collection and conveyance system design and operation Component Abalone tanks Internal Lateral Drains Southern Collection Channel Design criteria and details 2000 tanks (500 per module), each 20 m x 2.8 m and 50 mm water depth. 40 drains (10 per module) Each drain 335 m long & 600 mm wide with slope of 0.5% (1:200) Single 500 m long x 2 m wide flat bottom channel, separated into 4 sections (i.e. one per module) by penstocks. Normal depth at outlets 0.75 m. Operation and Performance Constant seawater flow through the tank at 2.6 L/s with daily flush of the tanks with tippers (1 L/s). Flow and flush direction alternate daily or as required. Only half the tanks can be flushed at a time. Regular flushing removes accumulated solids effectively (based on current practice at Yumbah Narrawong) and as such is considered adequate operation Wastewater velocity 0.43 m/s (north end) increasing to 1.17 m/s at southern discharge end. The Internal Lateral Drains remain relatively clean with most solids transported to the Southern Collection Channel during the morning tipper operation. Manual sweeping expected to be infrequent (i.e. bi-annually based on current practice at Yumbah Narrawong) and as such is considered adequate operation. There is potential to collect abalone shells and possibly excess feed at the discharge end of the. These options are discussed in Section 4. Wastewater velocity increases along each section to outlet up to 0.87 m/s at average flow and up to 1.0 m/s at peak daily flow. Solids accumulation is expected to occur in the channel, but less than experienced at Yumbah Narrawong. The solids consist primarily of fine sand, with most of the lighter organic matter normally being transported downstream. Periodic manual cleaning is required at Yumbah Narrawong using high pressure water jets to move the settled solids downstream into the solids removal facilities. This is labour intensive with high operating/maintenance costs. There are a number of options available to reduce and/or eliminate the need for manual cleaning. These are discussed in Section 4. October 2018 Page 7

16 3 Seawater and Wastewater Flows, Characteristics and Loadings 3.1 Seawater Flow Seawater is pumped through the 1000 t/a capacity Yumbah Nyamat abalone farm at a constant rate of 5.2 m 3 /s, based on 2.6 L/s through each of the 2000 tanks. Tipper seawater flow is 1.0 m 3 /s, based on daily flushing of each tank at 1 L/s. The peak hourly flow during the morning tank cleaning (tipper) operation is estimated to be 6.2 m 3 /s Characteristics Tables 3-1 summarises the ambient seawater quality at Yumbah Narrawong (median and 80 th percentile SS, VSS, NHx, TN, TP values) based on 86 samples tested over the period The seawater samples are taken at the inlet taps to the abalone tanks, and as such do not include solids that settle out in the inlet pipework. The table also shows the ANZECC & ARMCANZ (2000) toxicity and aquaculture trigger values. This long-term monitoring data indicates that ambient seawater quality at Yumbah Narrawong is well below the ANZECC & ARMCANZ trigger values. Table 3-1: Ambient seawater quality ( median and 80 th percentiles) at Yumbah Narrawong ( ) Location/Parameter Suspended Solids (mg/l) Volatile Suspended Solids (mg/l) Ammonia -N (mg/l) Total Nitrogen (mg/l) Total Phosphorus (mg/l) Median th percentile Maximum 37 Toxicity trigger value (ANZECC & ARMCANZ (2000) 99% species) Aquaculture trigger value (ANZECC & ARMCANZ (2000)) NA NA 0.50 NA NA NA NA NA October 2018 Page 8

17 3.1.3 Particle size distribution Figure 3-1 and Table 3-2 show the particle size distribution for seawater discharged in to the abalone tanks at Yumbah Narrawong on 24 August The seawater sample does not include sand that settles out in the inlet pipework. Background Aug17 Frequency (%) Undersize (%) Volume Density (%) Particle Size (µm) Cumulative Volume (%) Figure 3-1: Particle size distribution for seawater discharged to the existing abalone tanks at Yumbah Narrawong (24 August 2017) Table 3-2: Summary of particle size distribution (microns) for seawater inlet to abalone tanks at Yumbah Narrawong Location/Parameter 10 th percentile 20 th percentile Median 80 th percentile 90 th percentile 95 th percentile Inlet sand particle size a (microns) a Based on seawater inlet to abalone Yumbah Narrawong on 24 Aug Inlet sand loads The median inlet sand load at Yumbah Nyamat is 1.52 t/d, based on the median inlet sand concentration of 3.3 mg/l observed at Yumbah Narrawong and the Yumbah Nyamat average flow of 5.4 m 3 /s (i.e. includes tipper flow averaged over day). The 80 th percentile load is 3.2 t/d (based on the 80 th percentile sand concentration of 7.2 mg/l), and the maximum daily load is estimated to be up to about 17 t/d 9based on observed maximum recorded sand concentration of 37 mg/l. October 2018 Page 9

18 3.1.5 Wastewater flow The average daily wastewater flow and peak hourly flow are the same as the seawater flows, however the maximum instantaneous wastewater flow is estimated to be 13.6 m 3 /s, based on all pumps operating and the addition of an estimated 6.1 m 3 /s of rainfall collected during a 1 in 20-year ARI 5-minute rainfall intensity event Characteristics and loads Abalone Feed The annual abalone feed at Yumbah Nyamat is 1550 t/yr, based on a food to abalone conversion rate (FCR) of 1.45 (i.e. 2017/18 Yumbah Narrawong annual average, including 5% uneaten feed), and a total annual abalone production of 1075 t/a (i.e. including 75 t/a of morts). This average FCR corresponds to an efficient conversion rate 73% (i.e. excluding uneaten feed) and is similar to that achieved at Bicheno, Tasmania (ref 1) and South Africa (ref 2). Ref 1: Vandepeer, Abalone Aquaculture Subprogram Manufactured Diet Development, Project No. 96/385 (ISBN X), Abalone Aquaculture Subprogram (1 April 2005) Ref 2: Probyn et al, Characterisation of water quality in effluents of land-based abalone farms in the western Cape, South Africa, Aquaculture Environment Interactions Vol 9: (2017)). The composition of the feed used by Yumbah is a mixture of Semolina, soyflour and small quantities of fish oil, fishmeal, algae and vitamin similar to that used at Bicheno in the control feed trial, which contains 4.8 % nitrogen (70 t TN/yr) and 39% carbon (566 t C/yr). Lower FCR down to 1.28 are observed at Yumbah Narrawong during the peak growing season (December to March) and ongoing feeding trials continue to reduce the FCR further (i.e. approach the theoretical FCR of 1.0 observed in laboratory testing). The low FCRs achieved at Yumbah are considered best practice and significantly reduce the waste generated (i.e. abalone faeces) Abalone faeces The estimated average concentration of abalone faeces produced is 406 t/yr (2.4 mg/l), based on 73% of feed eaten (i.e. 2/3 of food pellets consumed end up as abalone and 1/3 as faeces. This value is the mass balance developed using the total nitrogen and carbon percentages observed in the feed, abalone and faeces for the control feed trial at Bicheno (Ref:1). The Yumbah Nyamat mass balance for SS, carbon, total nitrogen, ammonia and total phosphorus for the average flow and feed case is given in Appendix B. October 2018 Page 10

19 The annual faeces production is equivalent to a unit waste production rate of 1 g faeces/kg abalone per day, and corresponds to the unit value reported for 2-yr old abalone per day at seawater temperature of 16 o C (ref 3). Ref 3: Currie et al, Gastrointestinal evacuation time,..., of greenlip abalone is affected by water temperature and age, Aquaculture 448 (2015) pp )) The faecal material produced has similar density to seawater and readily solubilises in seawater, based on analysis of tank drainage channels and settling tank outlet monitoring. The ammonia concentration in the wastewater is estimated to be 0.07 mg/l, based 67 % solubilisation of faeces. This value is the same as the ammonia concentration observed at Yumbah Narrawong, the effluent ammonia reported at Bicheno of 0.03 to 0.07 mg/l (ref 1), and similar to that reported in South Africa of ~0.06 mg/l). (Ref 2). The carbon concentration in the wastewater is estimated to be 0.78 mg/l, which is equivalent to a BOD of < 2 mg/l Treated Wastewater (based on Yumbah Narrawong) Tables 3-3 summarises the ambient seawater quality and outlet characteristics of the solids settling ponds/tank (SST) at Yumbah Narrawong (median and 80 th percentile SS, VSS, NHx, TN, TP values) based on 86 samples tested over the period The table also shows the monitoring data for the for the corresponding period, together with the EPA licence values and the ANZECC & ARMCANZ (2000) toxicity and aquaculture trigger values. The Table also indicate that there is a net increase in nutrients through the abalone farm for both the median and 80 th percentile values, due primarily to the uneaten feed. There is also an increase in SS concentration through the farm for the 50 th percentile case but a decrease for the 80 th percentile case. This long-term monitoring data indicates that ambient seawater quality and discharge from the existing Yumbah Narrawong solids settling ponds/tank average about half the ANZECC & ARMCANZ trigger values and that the wastewater discharge easily complies with the existing EPA licence median limit. Figure 3-1 and Figure 3-2 show the total nitrogen and ammonia concentrations in the discharge from the existing Yumbah Narrawong solids settling ponds (SSPs) and channel (SEC) for the period , together with the EPA licence limit for each test. Figures 3-3 and 3-4 show typical particle size distributions for (1) ambient seawater; (2) wastewater discharged to and from the existing Yumbah Narrawong solids settling ponds (SSPs) and channel (SEC) for the period October 2018 Page 11

20 Table 3-3: Ambient seawater quality and solids settling ponds (SSPs) and channel (SEC) outlet characteristics (median and 80 th percentiles) at Yumbah Narrawong ( ) Location/Parameter Suspended Solids (mg/l) Volatile Suspended Solids (mg/l) Ammonia -N (mg/l) Total Nitrogen (mg/l) Total Phosphorus (mg/l) Median values Seawater (ambient) Solids settling ponds (SSPs) & tank (SST) outlets Increase (SST outletambient SW) 4.1 ~ ~ th percentile values Seawater (inlet) Solids settling ponds/tank (SST) outlets Change (SST outlets-sw inlet) EPA licence Annual median 5 NA Maximum 8 NA Toxicity trigger value (ANZECC & ARMCANZ (2000) 99% species) Aquaculture trigger value (ANZECC & ARMCANZ (2000)) NA NA 0.50 NA NA NA NA NA October 2018 Page 12

21 Nitrogen Levels in Sediment Pond Discharge Water at Yumbah Narrawong Total Nitrogen (mg/l) /11/01 7/11/02 7/11/03 7/11/04 7/11/05 7/11/06 7/11/07 7/11/08 7/11/09 7/11/10 7/11/11 7/11/12 7/11/13 7/11/14 7/11/15 7/11/16 7/11/17 EPA licence - maximum al lowance above background Background Pond 1 Outlet Pond 2 Outlet Pond 3 (SEC) Outlet Figure 3-2: Total nitrogen concentration in the discharge from the solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) 0.7 Ammonia Levels in Sediment Pond Discharge Water at Yumbah Narrawong 0.6 Total Ammonia-N (mg/l) /11/01 7/11/02 7/11/03 7/11/04 7/11/05 7/11/06 7/11/07 7/11/08 7/11/09 7/11/10 7/11/11 7/11/12 7/11/13 7/11/14 7/11/15 7/11/16 7/11/17 EPA licence - maximum al lowance above background Background Pond 1 Outlet Pond 2 Outlet Pond 3 (SEC) Outlet Figure 3-3: Ammonia concentration in the discharge from the solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) October 2018 Page 13

22 Background Aug17 Frequency (%) Undersize (%) Volume Density (%) Particle Size (µm) Cumulative Volume (%) SEC Inlet - DP3 only Volume Density (%) Frequency (%) Aug17 Undersize (%) Aug Particle Size (µm) Cumulative Volume (%) SST Inlet - DP3 + DP4 Frequency (%) Mar18 Frequency (%) Apr Volume Density (%) Particle Size (µm) 1, , Cumulative Volume (%) Figure 3-4: Typical particle size distributions for ambient seawater and wastewater discharged to the existing solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) October 2018 Page 14

23 SEC Outlet - DP3 only Frequency (%) Aug17 Undersize (%) Aug17 Volume Density (%) Particle Size (µm) Cumulative Volume (%) SST Outlet - DP3 + DP Volume Density (%) Frequency (%) Mar18 Frequency (%) Apr18 Undersize (%) Mar18 Undersize (%) Apr Cumulative Volume (%) Particle Size (µm) Figure 3-5: Typical particle size distributions for wastewater discharged from the existing solids settling ponds (SSPs) and channel (SEC) at Yumbah Narrawong ( ) October 2018 Page 15

24 3.1.7 Estimated loads based on testing on 19 July 2018 Table 3-4 summarises the estimated flows, suspended solids concentrations (sand, uneaten feed and faeces, total wastewater solids) and solids loads for various stages of the farm operation during the morning tipper operation and daily average, based on wastewater sampling and analysis undertaken at Yumbah Narrawong on 19 July Table 3-4: Summary of estimated flows, SS concentrations and loads for various stages of the farm for morning tipper operation and for daily average (19 July 2018) Location Flow (Seawater) Sand (ex seawater) Uneaten feed pellets and faeces Total Wastewater Solids (to treatment) Volume (ML) Concent. (mg/l) Load (kg) Concent. (mg/l) Load (kg) Concent. (mg/l) Load (kg) Tipper operation (morning) Farm Module Internal drain Tank Day (Average) Farm Module Internal drain Tank Based on wastewater sampling and analysis undertaken at Yumbah Narrawong on 19 July Mass balance summary Table 3-5 summarises the estimated return flows, concentrations and loads (SS, carbon, total N, ammonia and total P) for the average flow and feed case at Yumbah Nyamat, based on solids removal efficiency achieved at existing Yumbah Narrawong treatment facilities. The full mass balance for the average conditions case at Yumbah Nyamat, based on wastewater treatment using the existing Yumbah Narrawong solids removal facilities is given in Appendix B. October 2018 Page 16

25 Table 3-5: Summary of estimated return flows, concentrations and loads (SS, carbon, total N, ammonia and total P) for the average flow and feed case, based on solids removal efficiency achieved at existing Yumbah Narrawong solids settling facilities Characteristic Concentration Load Calc. (mg/l) Meas. (mg/l) Day kg/d Annual t/yr EPA licence limits ANZECC Trigger limits Comply Flow (ML) SS /8* yes Carbon Total N /0.4 yes Ammonia / /0.5 yes TP *VSS Table 3-6 summarises the estimated increase in concentrations and loads through the Yumbah Nyamat farm (SS, carbon, total N, ammonia and total P) for the average flow and feed case, based on solids removal efficiency achieved at existing Yumbah Narrawong treatment facilities. Table 3-6: Summary of estimated increase in concentrations and loads (SS, carbon, total N, ammonia and total P) through the Yumbah Nyamat farm for the average flow and feed case, based on solids removal efficiency achieved at existing Yumbah Narrawong treatment facilities Characteristic Concentration (mg/l) Load (t/yr) SS Carbon Total N Ammonia TP Note that the excess 5% equates to 3.7 t/yr TN compared with 15 t/yr for faeces (i.e. 25% of TN in faeces) October 2018 Page 17

26 4 Wastewater Management Issues The following issues impact on the selection and design of potential options: Variation in wastewater flow Variation in solids load Solids settling rates Solids settling in collection channels Solids Solubilisation Solids degradation Salt disposal Other issues, constraints and options 4.1 Variation in wastewater flow The variation in wastewater flow is summarised in Table 4-1. A design peak daily flow 1.55 m 3 /s is adopted for sizing each of the four solids removal facilities, based on treating the peak hour morning tank cleaning operation to remove 90% of solids down to 150 micron. The peak hydraulic flow capacity of the facilities is 3.4 m 3 /s (i.e. all inlet pumps operating or peak hourly morning flow plus rainfall on the tanks from a 1 in 20-year ARI 5 minute rainfall intensity event. Table 4-1: Summary of wastewater flows Flow Wastewater flow (m 3 /s) Comment Farm Module Minimum Average day Not including tank flushing Peak daily flow (design) Peak hour flow through 200 abalone tanks (during daily tank cleaning in morning) All inlet pumps operating Unlikely event Peak rainwater run-off to drains Maximum wastewater + peak rainfall runoff Rainfall 1 in 5-year ARI 5 min event Rainfall 1 in 20-year ARI 5 min event October 2018 Page 18

27 4.2 Variation in solids load Variation in sand concentration in seawater pumped to farm Table 4-2 summarises the variation in seawater characteristics (SS, ammonia, TP, TP, DO, ph) for the period 2001 to 2018 (86 samples). The Table shows that the suspended solids (SS) concentration in the seawater can vary significantly, ranging from 0-37 mg/l, with a median value of 3.3 mg/l. Elevated SS concentrations are observed during and following storm events, when the sand on the seabed is suspended with wave action. Table 4-2: Summary of ambient seawater characteristics Characteristic Suspended Solids (mg/l) Ammonia- N (mg/l) Total Nitrogen (mg/l) Total Phosphorus (mg/l) D.O. (%saturation) ph 20 th percentile Median th percentile th percentile th percentile Maximum Diurnal variation in abalone tank discharge characteristics As discussed in Section 2, most of the suspended solids entering the wastewater treatment plant are discharged during the abalone tank cleaning (tipper) operation (i.e. estimated ~80%), which occurs for a nominal 2-hour period in the morning. This is clearly shown on Table 4-2, which summarises wastewater discharge characteristics during the morning tank cleaning (tipper) operation and during the afternoon (i.e. no tank cleaning) at the Yumbah Narrawong farm on 19 July The following comments are made on the results of 19 July 2018 testing shown on Table 4-3: Elevated solids concentration of several hundred milligrams per litre (mg/l) are discharged from the tanks during the morning tank cleaning operation, of which ~44% are volatile solids The SS concentration discharged during the morning tank cleaning operation to the solids settling tanks was 36 mg/l, which was about four (4) times that observed during the afternoon (i.e. no tank cleaning) Ammonia and TN concentrations were higher in the afternoon (i.e. after the morning tank flush), and likely reflects the solubilisation of abalone faeces that have settled in the Southern Collection Channel TP concentrations were higher during the morning cleaning operation. October 2018 Page 19

28 Based on the above, there is potential scope for a dual wastewater treatment system involving separate treatment for the morning tank cleaning discharge and the discharge for the remainder of the day. Table 4-3: Summary of wastewater discharge characteristics during the morning tank cleaning (tipper) operation and during the afternoon (i.e. no tank cleaning) on 19 July 2018 Characteristic Suspended Solids (mg/l) Volatile Suspended Solids (mg/l) Ammonia- N (mg/l) Total Nitrogen (mg/l) Total Phosphorus (mg/l) BOD (mg/l) Seawater (Ambient) < 2 Tank cleaning (tipper) operation (2 hours in morning) Tank discharge Internal drain out Settling tank inlet < <2 Settling tank outlet No cleaning (tipper) operation (afternoon) Settling tank inlet <2 Settling tank outlet <2 4.3 Solids settling rates Solids settle in fluids based on the physical properties of the particle and the fluid (e.g. particle size, specific density and shape, and fluid density and viscosity). Historically particle settling velocity has been estimated using Stokes Law, however Stokes law is based on laminar flow and as such is not considered the best approach for particles >150 micron. Newtons Law for is preferred for settling in transitional and turbulent flow regimes. Both these laws assume smooth spherical particles. A refinement of these laws applies a shape factor to account for the observed difference between measured particle settling rates and calculated settling rates. I general terms, the larger the particle and the greater the specific density the faster particles falls, and the more angular and rougher the particle is the slower it settles (i.e. increased drag) Sand Figure 4-1 shows the predicted settling rate (cm/s) for sand/grit (SG 2.6) in freshwater versus particle size (micron). The preferred curve for sand settling in freshwater is considered to be the purple dashed line (i.e. Newton s law with shape factor). Sand at Yumbah Nyamat has a SG of 2.4 and is predicted to settle at a slower rate in seawater (i.e. 72 % of values shown on Figure 4-1). October 2018 Page 20

29 Source: Pat Herrick, Adam Neumayer, and Kwabena Osei - Hydro International, Grit Particle Settling Refining The Approach, Water Online 25 March 2015 Figure 4-1: Predicted settling rates (cm/s) for sand in freshwater versus particle size (micron). Table 4-4 shows the calculated settling velocities (cm/s) in seawater for sand with SG of 2.4 for different sand particle sizes using Newton s Law and different shape factors Table 4-4: Calculated settling velocities (cm/s) in seawater for sand with SG of 2.4 for different sand particle sizes using Newton s Law and different shape factors Particle size Settling Velocity (cm/s) Newton s Law with Shape Factor = 1 Newton s Law with Shape Factor = 2 Adopt for preliminary design 300 micron micron Food pellets Settling tests were undertaken in September 2018 on Yumbah Aquafeed (30% protein) pellets (nominal 5 mm x 5 mm x 1.5 mm, SG = 1.07) to determine the settling velocity in seawater for both dry pellets and pellets soaked for 12 hours. The settling velocity observed for dry pellets was 8.5 cm/s and for the 12-hour soaked pellet 6.5 cm/s. October 2018 Page 21

30 Based on these settling velocities observed feed pellets settle faster than sand with particle size less than about 500 micron. A preliminary design settling rate of 3 cm/s is adopted for sizing facilities to maximize removal of wet pellets, which provides an allowance for further solubilisation over time prior to settling Faeces The settling velocity of faeces is not known; however, it is expected to be low (i.e. <0.1 cm/s, similar to sand < 50 micron, due to its low relative specific weight. 4.4 Solids Settling in Southern Collection Channel The wastewater velocity in the flat bottom channel increases as the flow moves downstream up to 0.87 m/s at average flow and up to 1.0 m/s at peak daily flow. Generally, a minimum velocity of 0.65 m/s is required to prevent solids deposition in channels and pipelines, and typical flushing velocities (e.g. daily to weekly) are m/s. As such, solids deposition is expected to occur in the channel, particularly at the top end where the velocities are lowest. Experience at Yumbah Narrawong farm shows that up to 200 mm thick solids accumulation occurs. The solids consist primarily of fine sand (approximately 50% dry solids (DS), with most of the lighter organic matter normally being transported downstream. Periodic manual cleaning is required at Yumbah Narrawong using high pressure water jets to move the settled solids downstream into the solids removal facilities. This is labour intensive with high operating/maintenance costs. There are a number of options available to reduce and/or eliminate the need for manual cleaning, including: Provide sloping floor at top end to increase velocity above 0.65 m/s Periodic flushing at the top end with seawater (e.g. daily) Provide aeration and/or mixers to maintain solids in suspension Continuous removal with vacuum system (e.g. industrial pool cleaner). 4.5 Solids Solubilisation The pellets are designed to remain solid for at least 24 hours so that they are available to the abalone for feed. Experience at Yumbah Narrawong indicates that most (at least half) of the pellets remain whole (although swollen) on entering the existing solids settling facilities, however the pellets solubilise over time, as experienced in the settling ponds, thereby releasing organics and nutrients (including ammonia) in to the wastewater (refer Table 4-5). October 2018 Page 22

31 Table 4-5: 50 th percentile performance of Yumbah Narrawong solids settling ponds/tank (2001 to 2018) Location/Parameter Suspended Solids (mg/l) Ammonia -N (mg/l) Total Nitrogen (mg/l) Total Phosphorus (mg/l) Pond 1 In Out Pond 2 In Out Tank 3 In Out The solubility of abalone faeces is not available; however, it is expected that this waste will solubilise relatively quickly, based on experience in domestic sewage plants, especially given the small size. 4.6 Solids degradation Experience in the existing solids settling ponds/tanks at Yumbah Narrawong shows that the pellets and faeces degrade over time in the anaerobic conditions. This has potential to be an odour issue when the solids are periodically removed if the solids remain in the settling facilities for a prolonged time. 4.7 Salt in dewatered sludge requiring disposal Wastewater sludge dewaters to about 30% dry solids in the solids settling tank and storage pile (i.e. after removal from tank), based on experience at Yumbah Narrawong. The remaining 70% is seawater, which contains 3.5% salt. The estimated annual salt load in the dewatered sludge is expected to range from 9 t/a if all solids >300 micron are removed and up to 15 t/a if all solids >150 micron are removed (refer Table 4-6). October 2018 Page 23

32 Table 4-6: Summary of estimated annual solids loads for various solids removal efficiencies Solids removal option Annual settled sludge load Remove > 300 micron solids Remove > 150 micron solids Sand 27 t DS 107 t DS Uneaten feed pellets 80 t DS 80 t DS Total Wastewater Solids 107 t DS 187 t DS Seawater in dewatered sludge (@ 70% (by Wt) 250 t (m3) 440 t (m3) Salt load in 3.5% 9 t 15 t 4.8 Other issues Abalone shells can end up in drainage water which could block pumps Screens located in channels downstream of the abalone tanks block with weed (20 mm square openings) over time. October 2018 Page 24

33 5 Wastewater Treatment and Solids Handling Options 5.1 Objectives The principal objectives of the abalone wastewater treatment and solids handling facilities are: maximise removal of uneaten abalone feed to reduce organic load and nutrient concentrations discharged, and thereby ensuring that discharged wastewater does not cause environmental harm to the receiving coastal waters and complies with EPA discharge limits. separate treatment facilities for wastewater from each module prior to discharge to the marine environment to assist with maximising the biosecurity of the farm use wastewater processes and equipment that meets best wastewater industry practice provides efficient, reliable environmentally friendly and safe operation maximises segregation of wastes and reuse minimises solid waste material to be carted off-site for reuse/disposal. The wastewater treatment facilities are not designed to remove abalone faeces produced as the material has similar density to seawater and readily solubilises in seawater, based on analysis of tank drainage channels and settling tank outlet monitoring. 5.2 Potential Options The following options have been identified as being potentially applicable: Do Nothing option Solids Settling Ponds (as per original Yumbah Narrawong) Solids Settling Tanks (as per Yumbah Narrawong 2015 augmentation) Solids Settling Channels Vortex-type Solids Settling Tanks Screens and filters Other 5.3 Do Nothing option The design of Yumbah Nyamat involves farming abalone on land by passing seawater once through tanks prior to discharge back into a dynamic and dispersive environment of Portland Bay (i.e. minimal recirculation and associated build-up pf organics and nutrients). The predicted wastewater discharge characteristics for Yumbah Nyamat meet relevant receiving water guidelines with a good margin of safety (e.g. ANZECC trigger values) and the EPA licence conditions (i.e. similar to those observed at Yumbah Narrawong). As such, it could be argued October 2018 Page 25

34 that there is a case for the do nothing option at the discharge point, which is currently Standard Practice in South Australia. However, no removal of pellets is undertaken. As such, no reduction in organics and nutrients is achieved (i.e. no waste minimisation). Yumbah have taken the view that this option should not be carried forward, despite the fact that wastewater treatment is not required from a marine environmental protection perspective Assessment Advantages Disadvantages No CAPEX and OPEX Does not achieve waste minimisation objective (i.e. no pellets removal to reduce organics and nutrients discharged) No solid/salt waste disposal issues 5.4 Solids Settling Ponds (SSPs)(as per Yumbah Narrawong) Description The major features of the option (based on the original Yumbah Narrawong ponds) are: Four separate settling ponds (i.e. one for each module) with nominal average hydraulic retention time 60 minutes at 1.55 m 3 /s. Nominal size 80 m x 40 m x 2 m deep (capacity ~5400 m 3 ) Solids removal performance a significant proportion of solids > 150 micron Impervious HDPE liner Reduce short-circuiting by optimising separation distance between inlet and outlet and by providing baffles to lengthen flow path Operation Wastewater continuously enters the pond at one end and overflows at the opposite end. Periodically the accumulated solids are removed by either taking the pond offline and dewatering the sludge prior to removal with mechanical equipment (e.g. bobcat) or removed using vacuum sucker truck (this option ideally requires a deeper pond with sludge hopper) October 2018 Page 26

35 5.4.3 Assessment Advantages Disadvantages Simple, robust and reliable Large area required to provide long retention time to compensate for short-circuiting issue Infrequent cleaning required Pellets solubilise over time releasing ammonia back into the wastewater discharge to the marine environment Low operating costs Potential odour issue during periodic removal of anaerobic sludge 5.5 Solids Settlement Tanks (as per SECs at Yumbah Narrawong) Description The major features of the option (based on the facility installed for the Yumbah Narrawong 2015 augmentation: Four separate settling tanks (i.e. one for each module) with nominal average hydraulic retention time of about 3 minutes at 1.55 m 3 /s Nominal size 20 m x 11 m x 1.2 m deep (capacity ~270 m 3 ) Solids removal performance a significant proportion of solids > 150 micron Concrete tank with access ramp for excavator/bobcat to remove sludge Reduce short-circuiting by optimising separation distance between inlet and outlet and by providing baffles to lengthen flow path Operation Wastewater continuously enters the pond at one end and overflows at the opposite end. Pellets and sand > ~ 150 micron settle Periodically the accumulated solids are removed by taking the tank offline and using mechanical equipment (e.g. bobcat) to remove the sludge to land for drying and stockpiling. Solids consist of fine sand, anaerobic sludge and weed with about 30% solids content Periodic sludge removal is an odourous operation due the disturbance and mechanical handling of the anaerobic material. October 2018 Page 27

36 5.5.3 Assessment Advantages Disadvantages Less area required than ponds Medium area required to provide retention time to compensate for shortcircuiting issue Simple, robust and reliable Partial solubilisation of pellets over time releasing ammonia back into the wastewater discharge to the marine environment Infrequent cleaning required Potential odour issue during periodic removal of anaerobic sludge Low operating costs Reduced solids removal over time with reduced retention time due to build-up of solids in tank 5.6 Solids Settling Channels Description This option is based on the traditional wastewater grit removal channel system that provides a long channel to establish plug flow to minimise short-circuiting with a low constant velocity to enable solids to settle out. The major features of the option are: Four separate channels (i.e. one for each module) with an average hydraulic retention time of 116 seconds during normal operation (i.e. 1.3 m 3 /s), and 98 seconds at design daily peak flow (i.e m 3 /s experienced during daily flushing of abalone tanks) Peak hydraulic capacity of each 3.4 m 3 /s Nominal size 35 m long x 3.6 m wide and 1.2 m side water depth (SWD) (capacity 150 m 3 ) Outlet weir 0.4 m high Concrete tank with outlet overflow weir to control level and maximum fall of particles to enable capture at 0.8 m Operation Wastewater continuously enters one end and flows along the channel to the opposite end at a velocity of 0.30 m/s at average daily flow; at 0.36 m/s at design peak daily flow (i.e. peak hour morning tank cleaning). Estimated peak velocity is 0.63 m/s at maximum flow of 3.4 m3/s (i.e. all pumps operating and peak rain event (1 in 20 year ARI 5 minute duration). Most pellets and 90% of sand down to 150 micron settle out as the flow moves down the channel at the low velocity. The pellets settle out first at the inlet end (settling rate >6.5 October 2018 Page 28

37 cm/s), followed by the larger sand particles and then the smaller sand particles near the outlet. Peak velocity of 0.63 m/s (during short-term peak rainfall event) is less than the minimum self-scouring velocity of 0.76 m/s for 150 micron particles. As such solids washout downstream is not expected to be an issue. Estimated average daily depth of settled solids on the channel floor is about 3 mm/d and 5 mm/d depth at 90 th percentile seawater SS concentration, and 16 mm/d for maximum inlet sand SS of 37 mg/l. Periodically the accumulated solids are removed by either taking the tank offline (e.g. weekly to monthly) and using mechanical equipment (e.g. bobcat) to remove the sludge to land for drying and stockpiling, or routine cleaning (e.g. daily to weekly) using mechanical scraper, vacuum system or equivalent) Solids consist of fine sand, pellets and ribbon weed with about 30% solids content. The nature of the sludge (i.e. aerobic/anaerobic will depend on the frequency of cleaning. Periodic sludge removal has potential to be an odourous operation is the sludge is removed infrequently (i.e. anaerobic material) Assessment Advantages Less area required than rectangular tanks due to minimising short-circuiting Superior and predictable solids removal performance Disadvantages Relatively high civil costs for large concrete channels Potential for partial solubilisation of pellets over time if solids not removed regularly, which releases ammonia back into the discharge Simple, robust and reliable Increased sand removal resulting in increased salt in sludge and associated salt disposal issue Low operating costs Potential odour issue if infrequent periodic removal of anaerobic sludge 5.7 Vortex-type Solids Settling Tanks Description Solids in the wastewater can also be removed in devices that use a vortex-flow pattern. Figures 5-1 and 5-2 illustrate two types of devices that are typically used. Standard vortex tank (current industry standard) (Figure 5-1). Wastewater enters and exits tangentially. A rotating turbine maintains constant flow velocity and produces a toroidal-flow path for the particles to settle by gravity into the hopper. Solids are removed by a submersible pump and dewatered in a classifier/hydrocyclone. There are a number of propriety units October 2018 Page 29

38 available include: Pista grit tank (from Smith and Loveless), Jeta tank and Meva tank. The units are generally of concrete construction and cast in-situ. A disadvantage of this option is the high capital cost of the long inlet channel required to establish ideal inlet flow conditions. Figure 5-1: Conventional vortex solids settling tank (e.g. Pista Grit) Grit King (from Hydro International) (Figure 5-2). This system is a later generation of the traditional units. Wastewater enters the cylindrical tank tangentially, either mid height (preferred) or at the top, causing a rotational flow path around a dip plate. The flow spirals down the wall as the solids settle out by gravitational forces and forces created by the rotating flow (green arrow). The grit collects in a central hopper as the centre cone deflects flow away from the base, up and around the central shaft into the inside of the dip plant (blue arrow). The upward flow is reported to rotate at a slower velocity than the outer downward flow, thereby resulting in in a shear zone which removes finer particles. The concentrated settled solids underflow is pumped to a classifier/hydrocyclone for dewatering. The Grit King (or equivalent) is the preferred vortex settling tank for the following reasons: Smaller tank than traditional vortex grit tank No long inlet works to create ideal flow path resulting in lower civil costs No moving parts (no need to periodically decommission to maintain internal equipment). The major features of the option are: Four separate 9.6 m diameter Grit King tanks (or equivalent) (i.e. one for each module) based on flow of 1.55 m 3 /s 1.2 m dia inlet pipe and 2.4 m wide rectangular outlet box The Grit King achieves 95% removal down to 150 micron at 1.3 m 3 /s (average daily flow) and 90% removal down to 150 micron at 1.55 m 3 /s (peak daily flow) The tanks are available in materials ranging from painted mild steel (preferred, used at Karratha desalination plant), 316SS (expensive), and Duplex (very expensive). Due to the metal tank size they would be installed in a concrete tanks October 2018 Page 30

39 A submersible pump transfers settled solids collected in the bottom hopper to above ground solids classifier/hydrocyclone for dewatering and cartage to disposal area. October 2018 Page 31

40 Figure 5-2: Grit King vortex solids settling tank Operation The unit operates continuously as described above, with at least daily pump out and dewatering of removed solids Estimated headloss at 1.55 m 3 /s is < 180 mm Solids are expected to dewater to about 30% solids content. Estimated average daily volume of settled solids removed per unit is about 0.2 m 3 /d and the peak <1 m 3 /d Assessment Advantages Smallest area required of gravitational settling processes/options High capex Disadvantages Highest removal efficiency of gravitational processes/options and predictable performance Can be designed to remove a range of particle sizes (e.g micron) Simple, robust and reliable October 2018 Page 32