Hence, most commentators will indicate a range of values for effluent quality and maybe put forward a typical concentration.

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1 NOTES on SEPTIC TANK EFFLUENT QUALITY Prepared By: Ian Gunn, On-Site NewZ 25 August Background Information on septic tank effluent quality is particularly hard to come by as: the amount of work required to effectively sample a septic tank unit is both substantial and costly; there is no uniformity in input quality and effluent quality from one septic tank to another because of different loading patterns and waste outputs from individual houses; there are a variety of different tank configurations and capacities which can lead to wide variations in effluent quality; and maintenance frequency and variations for individual tank units can vary widely and affect the overall treatment unit performance. Hence, most commentators will indicate a range of values for effluent quality and maybe put forward a typical concentration. A sampling of examples from the literature is set out below. 2.0 On-site pre-treatment unit performance standards (for discussion, USA, 1998) These standards [Attachment 1] include suggested effluent quality levels for BOD 5, TSS Tot-N and FC for septic tanks with and without effluent outlet filters. 3.0 Compilation of On-site Treatment Effluent Quality Information Attachment 2 sets out tables of information from three references which include details on septic tank effluent quality ranges as follows: A: TP58 Draft for Edition 3 (July 2003) B: NSW Guidelines (1998) C: Horizons.mw Draft Values (8 February 2008). 4.0 Mark Gross, PhD University of Arkansas, University Curriculum Development for Decentralized Wastewater Management (2005) This PowerPoint presentation [Attachment 3] provides data on septic tank effluent quality from major US sources dealing with on-site wastewater management. 5.0 On-Site Wastewater Treatment and Recycling Review of the 1 st International Conference, Fremantle WA, February 2004 A review of two papers [Attachment 4] discusses septic tank effluent quality. These reviews were originally published within On-Site NewZ Special Report 04/1 April Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 1

2 ATTACHMENT 1: On-site pre-treatment unit performance standards (for discussion, USA, 1998) Standard BOD 5 g/m 3 TSS g/m 3 Total Nitrogen % reduction Faecal Coliforms cfu no./100ml TS 1 Primary treatment TS 1u - unfiltered TS 1f - filtered NA NA 10,000,000 10,000,000 TS 2 Secondary treatment NA 50,000 TS 3 Tertiary treatment NA 10,000 TS 4 Nutrient reduction TS 4n % 10,000 TS 5 Bodily contact disinfection % 200 TS 6 Wastewater reuse % 14 TS 7 Near drinking water % <1 (NO 3 -N 10 g/m 3 ) (Total coliforms <50) [Gunn Armidale On-site 03 Keynote Address] Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 2

3 ATTACHMENT 2: A: TP58 Draft for Edition 3 [July 2003] Table 7.1 Effluent Quality Ranges On-site Treatment Options Treatment Unit Concentration g/m 3 FC BOD 2 TSS NH 3 NO 3 PO 4 No. per 100 ml Raw Wastewater 250 to to to 40 <1 10 to to Raw Greywater 180 to to 160 Traditional Septic Tank Septic Tank (poor operation) 170 to to to 60 <1 10 to to Septic Tank (good operation) 120 to to to 30 <1 7 to Greywater Tank (average operation) 50 to to 50 Digestive Tank (average operation) 60 to to 60 Two stage septic Tanks (in series) 70 to to 60 Conventional Septic Tank Septic Tank with 70 to to 30 Outlet Filter S T plus [note 3] Intermittent Sand Filter <10 <10 4 x 10 2 to 10 3 S T plus Recirculating Sand Filter 4 to 8 2 to 6 2 to to 10 4 S T plus 30 (ave) Recirculating Textile to 30 (ave) 10 3 to 10 4 Filter [note 6] AS AWTS [note 4] 5 to 50 5 to 100 < x 10 3 AS -AWTS Plus Sand Filter <10 <10 < Tertiary Disinfection [note 7] (This table is based on Table 6.1 in TP 58 Edition 2, but has been revised and updated) NOTES. 1. Data based on indicative values from the literature (and in some cases on estimates) and NOT on recorded NZ information. 2. The effluent quality obtained from the more sophisticated treatment system is reliant upon the system design, loading rate and being correctly operated and maintained. 3. ST refers to Septic Tank. 4. AS- AWTS refers to activated sludge aerated treatment plant. 5. Treated wastewater output quality can vary significantly from the above typical values and is dependent upon the wastewater influent composition. 6. The lower nitrate concentration is following an additional nitrate reduction cycle. 7. The level of disinfection and reduction in indicator organisms is dependent upon the level of and type of disinfection. Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 3

4 ATTACHMENT 2 [ct d]: A: TP58 Draft for Edition 3 [July 2003] (ct d) Table Average Septic Tank Effluent Concentrations of Selected Parameters from a Range of Commercial Establishments Source BOD (mg/l) COD (mg/l) TSS (mg/l) Wastewater Composition TKN TP (mgn/l) (mgp/l) Oil/Grease (mg/l) Restaurant Restaurant Restaurant Restaurant Restaurant Restaurant Temp ( o C) Bar/Grill Motel Source: Ref 5 based on Siegrist et al Table 7.9 Typical Performance Values for Conventional Septic Tanks and Secondary Sand/Textile Filter Systems Septic Tank with Intermittent Sand Recirculating Sand Textile Filter outlet filter Filter Filter BOD mg/L <10 mg/l <10 mg/l <15 mg/l TSS mg/l <10 mg/l <10 mg/l <15 mg/l NH mg/l 0.5 to 10 mg/l 0-15 mg/l 0 5 mg/l NO 3 <1 mg/l mg/l 30 mg/l (average) Total N mg/l (40% - 50% reduction) PO 4 7 mg/l FC ,000 per 100mls /100mls (99% reduction) [note 3] Note: 1. Based on a range of values from the literature. 2. Nitrate reduction is an optional feature for textile filters. 3. The number of faecal coliforms following treatment dependent upon influent nos. ph 5 30 mg/l [Note 2] /100mls (99% reduction) [note 3] B: NSW Guidelines [1998] Table 11: Expected Quality of Wastewater after Treatment in a Septic Tank Parameter Concentration Biochemical oxygen demand (BOD) Suspended Solids (SS) Total Nitrogen (N) Total Phosphorus (P) Faecal coliforms 150 mg/l 50 mg/l mg/l mg/l cfu/100 ml Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 4

5 ATTACHMENT 2 [ct d]: B: NSW Guidelines [1998] (ct d) Table 14: Expected Quality of Wastewater after Treatment in an AWTS NSW Health Certification Parameter Concentration* Failure Indicator Biochemical oxygen demand (BOD) <20 mg/l >50 mg/l Suspended Solids (SS) <30 mg/l >50 mg/l Total Nitrogen (N) mg/l Not applicable Total Phosphorus (P) mg/l Not applicable Faecal coliforms Up to 10 4 cfu/100ml Not applicable (non-disinfected effluent) Faecal coliforms <30 cfu/100ml >100 cfu/ml (non-disinfected effluent) Dissolved oxygen >2 mg/l <2 mg/l *Design figures might not be indicative of long-term operational characteristics C: HORIZONS.MW Draft Values [8 February 2008] Parameter Septic tank Improved septic tank Secondary treatment BOD SS Oil & Grease FC cfu s x NH 3 as N <1 -- TKN NO Total N PO DRP Total P Advanced secondary treatment Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 5

6 ATTACHMENT 3: Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 6

7 ATTACHMENT 3 [ct d]: Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 7

8 ATTACHMENT 3 [ct d]: Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 8

9 ATTACHMENT 4: On-Site Wastewater Treatment and Recycling Review of the 1 st International Conference, Fremantle WA, February 2004 [On-Site NewZ Special Report 04/1 April 2004] Paper 1: Effluent quality from 200 on-site sewage systems: Design values for guidelines (K.J. Charles, School of Civil & Environmental Engineering, University of New South Wales, Sydney NSW) Effluent quality is a most significant factor affecting the performance of land application systems in on-site domestic wastewater management. High levels of BOD and SS affect the infiltration capacity of the soil, and can potentially lead to system failure. High nitrogen and phosphorus levels can lead to vegetation impacts, including growth stress and promotion of weeds. This paper collates the results from 6 separate sampling and testing projects in the Sydney Catchment Authority area. 48 septic tanks (35 being domestic, the rest communal) and 143 AWTS units were assessed. The septic tanks were 10 years or more old, and sampling results included a range of sample events, including single grab samples up to routine sampling over one year. AWTS units had been in operation between 6 months and two years, and had undergone a maintenance check within the 3 months before sampling. Current NSW on-site system guidelines are based upon septic tank effluent quality as follows: BOD 5 150g/m 3 SS 50 g/ m 3 Tot-N 50-60g/m 3 Tot-P g/m 3 Thermo-T Coliforms cfu/100ml Results of the sampling programme indicate that actual septic tank effluent quality is much stronger than that represented in the guidelines and in the literature. Only 13% of systems recorded SS levels within the current guidelines, and 33% for BOD. The respective values for Tot-N and Tot-P were 23% and 40%. The implications of this are that up to 87% of land application system failure may be related to suspended solids overload. Up to 77% of soil systems may be inadequately designed for nutrient uptake. The study averages on septic tank effluent quality were as follows: BOD g/m 3 SS 379 g/m 3 Tot-N 160 g/m 3 Tot-P 21 g/m 3 Thermo-T Coliforms 10 6 cfu/100ml Concentrations may not, of course, represent the actual loading in the soils system, as it is total mass daily load that is important. Although very little hydraulic flow data was available from this particular study, indications are that the NSW guidelines under represent organic and nutrient loads passing to land disposal areas in around 50% of systems. This is based on the fact that residential septic tank flows from the limited data in the study show 132 litres/person/day compared to the 180 litres/person/day in guidelines. AWTS units performed much better than septic tanks in terms of complying with guidelines. The recorded level of compliance was 49%, with free chlorine levels being non-complying in 22% of systems. Average effluent coliforms levels were high in the non-complying systems, with average BOD and SS within guideline levels. However, these AWTS results indicate a substantial improvement on 1995 performance levels, with a reported 5% compliance level (the equivalent of today s results being 42% against the 1995 assessment criteria). Given the reported high failure rates of septic tank effluent land application (soil soakage) systems in NSW, it would appear desirable that the 80 th percentile effluent strength would provide a relevant basis on which to base design sizing of such systems. This would be: BOD g/m 3 SS 660 g/m 3 Tot-N 250 g/m 3 Tot-P 36 g/m 3 As the thermo tolerant coliform values found from the study were the closest to the guidelines, they can remain as current for design purposes. Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 9

10 Additional sampling is now under way to confirm the results of the current programme, and to investigate baffled septic tanks as well as nutrient outputs from AWTS units. Paper 2: Performance of on-site wastewater treatment systems in Finland (K. Kujala-Räty, Finnish Environment Institute, Helsinki) Some 19% of Finnish people use on-site wastewater servicing, usually septic tank and simple soil infiltration systems. In order to meet increasing performance standards for on-site systems, alternative treatment units prior to land application have been investigated. Some 48 on-site systems have been monitored over two years 1998 to An initial finding of the results of sampling was the very high variability in septic tank effluent quality, between neighbouring septic tanks sampled at the same time, and between successive samples in one septic tank taken at long intervals between samplings. Grab sampling was found to be quite inadequate to reflect average quality from a system. BOD was found to change from 38 g/m 3 (morning) to 110 g/m 3 (afternoon) at one dwelling. [Note: Results in the paper were expressed as BOD 7 and not BOD 5.] On the basis of 23 septic tanks and 33 composite samples over 8 hours, average values of septic tank effluent quality were: BOD g/m 3 SS 70 g/m 3 Tot-N 110 g/m 3 Tot-P 16 g/m 3 Faecal Coliforms 4.7 x10 6 [On-Site NewZ Note: The septic tank units consisted of 2 or 3 cylinders in series. The staged settling approach is probably the reason for the good suspended solids performance.] The 28 sand filter systems monitored included conventional buried sand filters (13 systems), buried sand filters with a phosphorus adsorbing layer (9 systems), and sand filters with a phosphorus adsorbing cassette (4 systems). Four samples were taken throughout the day (6am to 8pm) and composited. BOD 7 effluent quality was as follows: conventional sand filters 7(mean) 8(median) Sand filters with P adsorb 16(mean) 5(median) layer Sand filters with P adsorb 17(mean) 11(median) cassette Overall sand filter BOD effluent quality was good, 24 plants less than 30 g/m 3, and 4 plants less than 60 g/m 3. Suspended solids, Tot-N, and faecal coliform removal performance correlated well with BOD removal performance. However, the sand filters ability to remove phosphorus was variable, with only half the filters achieving good or satisfactory removal. The median Tot-P in the effluent was 2.6 g/m 3, which seems good. However, Tot-P removal is essentially unpredictable. The filters with P-adsorbing material did not prove to have significant phosphorus removal benefit over conventional sand filters. Septic Tank Effluent Quality Notes Ian Gunn [25 August 2014] Page 10