Faecal Sludge Management

Transcription

1 Sandec Training Tool 1.0 Module 5 Faecal Sludge Management Eawag: Swiss Federal Institute of Aquatic Science and Technology

2 Definitions & Objectives What is Faceal Sludge Management? (FSM)? Faecal Sludge Management deals with the management of sludges from on-site sanitation systems, while wastewater management deals with sewered sanitation. Faecal sludge may be treated in separate treatment works or co-treated with sludges produced in wastewater treatment plants. Sandec Training Tool 2

3 Cesspit Combined Sewer Faecal Sludge Faeces Septage Sewage Sewer Sewerage Sludge Sullage Definitions An enclosed container used for storing sewage. A sewer system that is designed to carry both blackwater from homes and stormwater (rainfall). Combined sewers must be much larger than Separate Sewers to account for the high volume. Is the general term for the undigested or partially digested slurry or solid that results from the storage or treatment of blackwater or excreta Refers to (semi-solid) excrement without any urine or water Liquid and solid material pumped from a septic tank, cesspool or other primary treatment source. General name given to the mixture of water and excreta (urine and faeces), although more technically it should be referred to as blackwater. An open channel or closed pipe used to conveying sewage Definitions & Objectives All the components of a system used for collecting, transporting and treating sewage (including pipes, pumps, tanks, etc.) The thick, viscous layer of materials that settles to the bottom of septic tanks, ponds, and other sewage systems. Sludge is comprised mostly of organics, but also sand, grit, metals, and various chemical compounds. Old word for greywater: includes wastewater from cooking, washing, and bathing, but does not include any excreta. Sandec Training Tool 3

4 Definitions & Objectives On-site vs. sewered FS management Sewered sanitation On-site sanitation Excreta Wastewater treatment plant Effluent to soakage, drains or sewers Septic tanks Latrines Sludge treatment Liquid to discharge into receiving waters Effluent to agricultural use or discharged into receiving waters Biosolids to agriculture for soil conditioning and fertilisation Sandec Training Tool 4

5 Introduction Which parameters are used to characterise FS? ph C/N TS EC TVS TKN Heavy metals Helminth eggs FC (MPN) AN BOD/COD Sandec Training Tool 5

6 What are the daily per capita quantities for FS? Introduction Parameter Septage 1 Public toilet sludge 1 Pit latrine sludge 2 Fresh excreta BOD [g/cap day] TS [g/cap day] TKN [g/cap day] Volume [l/cap day] 1 2 (includes water for toilet cleansing) (faeces and urine) 1 Estimates are based on a faecal sludge collection survey conducted in Accra, Ghana. 2 Figures have been estimated on an assumed decomposition process occurring in pit latrines. According to the frequently observed practice, only the top portions of pit latrines (~ m) are presumed to be removed by the suction tankers since the lower portions have often solidified to an extent which does not allow vacuum emptying. Hence, both per capita volumes and characteristics will range higher than in the material which has undergone more extensive decomposition. Sandec Training Tool 6

7 Systems & Technologies What influences the character of Faecal Sludge? Tank emptying technology + pattern Storage duration (months to years) Performance of septic tank Faecal sludge is a highly concentrated and variable material. Treatment system should Quality be of designed Faecal Sludge on a case-to-case basis. Admixtures to FS (e.g grease, kitchen / solid waste) Temperature Intrusion of groundwater Sandec Training Tool 7

8 Systems and Technologies What are the processing steps (functional groups) and technologies in sanitation? User Interface Collection and Storage/ Treatment Conveyance (Semi-) Centralised Treatment Use and/or Disposal Dry Toilet Urine Diverting Dry Toilet Urinal Pour-Flush Toilet Flush Toilet Urine Diverting Flush Toilet Single Pit Single VIP Dehydration Vaults Septic Tank Composting Chamber Anaerobic Baffled Reactor Anaerobic Filter etc. Human-Powered Emptying and Transport Motorized Emptying and Transport Simplified Sewers Small-Bore Sewer Conventional Gravity Sewer Jerry Can/Tank etc. Anaerobic Baffled Reactor Anaerobic Filter Trickling Filter Waste Stabilisation Ponds Activated Sludge Constructed Wetland Co-composting etc. Application of Urine Application of Dehydr. Faeces Compost Irrigation Aquaculture Soak Pit Leach Field Land Application Surface Disposal Only selected combinations of technologies will lead to functional systems. etc. Sandec Training Tool 8

9 Systems & Technologies What are the process steps in FS management? User Interface Collection and Storage/ Treatment Conveyance (Semi-) Centralised Treatment Use and/or Disposal Emptying / Haulage Treatment Reuse / Storage Sandec Training Tool 9

10 Systems & Technologies What are the major technologies for solid-liquid separation and FS treatment? Solid-liquid separation Secondary treatment Sandec Training Tool 10

11 Co-composting Municipal solid waste Mixing ratio: 1:2 to 1:10 Faecal sludge Thermophilic Co-composting C is effective for pathogen destruction valuable soil conditionercum-fertilizer Safe reuse in agric. 90 days is long enough for the inactivation of all helminth eggs. Sandec Training Tool 11

12 Systems & Technologies Planted drying bed Land requirement: ~ 0.03 m 2 /cap Operation Application rate: up to 250 kg/m 2 /year Application frequency: 1-2/week Desludging period: 2-3 years Vegetation cattails, reeds or bulrushes (~ 8 shoots/m2) Filter bed Large gravel (d=20mm): 25 cm Fine gravel (d=5mm): 25 cm Sand: 10 cm Underdrain Hollow concrete blocks Perforated PVC pipes Percolate and biosolids usually need further treatment Depends on sludge contamination and local discharge regulations Sandec Training Tool 12

13 Systems & Technologies Unplanted drying bed Sludge application depth: ~25-30 cm TS loading: ~ kg TS/m 2 *a Percolate quantity: ~50-80% of FS volume Drying period to attain 40% solids content: ~8-12 days (dry weather) Land requirement: ~ 0.05 m 2 /cap (assuming a 10-day cycle) Both, percolate and biosolid need further treatment! Sandec Training Tool 13

14 Systems & Technologies Settling/thickening tanks Settling/thickening units operated alternatively (e.g. 4 weeks loading / 4 weeks drying) Performance of the tanks strongly depends on the plants state of maintenance and operation Problem when treating fresh public toilet sludges: bad settling behavior! Sandec Training Tool 14

15 Faecal sludge Systems & Technologies Comparison of sedimentation/settling ponds vs. settling tanks Sedimentation ponds: 8-12 month loading / resting cycles (e.g. with inpond drying of solids) Settling tanks: 2-4 month loading / resting cycles (separated solids e.g. To sludge drying beds or co-composting) Characterization Settlingthickening tanks Settling ponds Suspended solids (SS) 60% > 95% BOD and COD (unfiltered) 3 50% 70 95% BOD (filtered) 18% 45% Sandec Training Tool 15

16 Systems & Technologies Anaerobic digestion + Biogas extraction energy production, light, cooking - Mechanization level higher than for e.g. pond systems - Higher operation and maintenance requirement Sandec Training Tool 16

17 Systems & Technologies Anaerobic vs. Aerobic digestion Organic Material (high BOD,COD) Influent Aerobic Anaerobic Reduced BOD, COD CO 2, H 2 O, NO 3-, SO 4 2-, PO 4 3- Dissolved BOD, COD CO 2, CH 4, N 2, NH 4+, H 2 S, PO 4 3- Aerobic Anaerobic Example of Application Trickling Filters, Oxidation Ponds Anaerobic Reactor Carbon Balance 50% CO 2 50% Biomass 95% CH 4 +CO 2 (=Biogas) 5% Biomass Energy Balance 60% Biomass 40% Heat production 90% Retained in CH 4 5% Biomass 5% Heat production Biomass Production Fast Slow Sandec Training Tool 17

18 Systems & Technologies Waste stabilisation ponds FS is usually pre-treated for solids-liquid separation (e.g. in ponds or tanks) Biosolids have to be treated to satisfy safe hygienic standards but can be reused as soil conditioner in agriculture Effluent use in agriculture is not possible due to its high salinity. Sandec Training Tool 18

19 Systems & Technologies FS co-treatment with wastewater Problems with Waste-Stabilization Ponds: Variable Effects and expected problems SS - Sludge settling and consolidation More frequent solids removal and handling Short-circuiting of flow NH4 / NH3 - Ammonia toxicity due to high concentration in undigested FS. Inhibition to the development of facultative and maturation pond conditions - Eye irritation Colouration - Dark colour of FS supernatants prevents light penetration Algal growth and hence facultative or maturation pond conditions may not evolve Sandec Training Tool 19

20 Co-treatment of FS and Wastewater in Activated Sludge Plants Sandec Training Tool 20 Sandec Training Tool 20

21 Primary Treatment Process Co-treatment of FS and Wastewater in Activated Sludge Plants According to ATV (1985), two conditions must be met if FS is to be co-treated with wastewater: FS should be diluted with the wastewater at least 20 times. The capacity of a sewage treatment plant should be designed for at least 600 kg BOD/d to avoid unstable treatment performance Activated Sludge Process The following impacts have been observed and reported in treatment plants overloaded with faecal sludge: Decrease in O2 content in aeration units Odour and foaming problems in aeration units Scum build-up in clarifiers - A brownish-yellowish colouring of the effluent Sandec Training Tool 21 Sandec Training Tool 21

22 Review Review FS management deals with the management of sludges from on-site sanitation systems FS may be treated in separate treatment works or co-treated with sludges produced in wastewater treatment plants On-site sanitation (OSS) systems are the predominant form of excreta treatment installations in urban centres of industrializing countries. Faecal sludge management has to cope with a number of challenges, namely health threats posed by manual emptying of pits, indiscriminate disposal and by no or inadequate treatment of sludges. Sandec Training Tool 22

23 Credits Credits Publisher: Eawag, Sandec: Department of Water and Sanitation in Developing Countries, P.O. 611, 8600 Dübendorf, Switzerland, Phone +41 (0) , Fax +41 (0) Editors: Doulaye Koné Concept and Content: Manuel Henseler, Benjamin Hemkendrei and Karin Güdel Layout: Benjamin Hemkendreis and Manuel Henseler Copyright: Eawag/Sandec 2008 Eawag/Sandec compiled this material, however much of the text and figures are not Eawag/Sandec property and can be obtained from the Internet. The modules of the Sandec Training Tool are not commercial products and may only be reproduced freely for non-commercial purposes. The user must always give credit in citations to the original author, source and copyright holder. This Powerpoint presentation and its matching lecture notes are available on the Sandec Training Tool CD and can be ordered at: Sandec Training Tool 23