Integrated Digestion and Nutrient Recovery to Enhance Value Extraction from Faecal Sludge Treatment

Transcription

1 Integrated Digestion and Nutrient Recovery to Enhance Value Extraction from Faecal Sludge Treatment Anna Trego* C. Rose*, S. Connelly, R. Kennedy-Walker, V.T. Nguyen, D. Hughes, S.G. Shin, C. Patterson, J. Kabika, S. Verdi, A. Parker, K. Kar, B.L. Mehta, D. Raffo, N. Osbert, E. Clifford, J. Amezaga, C.A. Biggs, E. Cartmell and G. Collins

2 A New Global Agenda UN, 2016 To achieve adequate and equitable sanitation for all and end OD with special attention to women and girls Slide 1/20

3 Integrated Nature of Sustainable Development Slide 2/20

4 Consortium Motivations Protect water resources & public health Use robust & locally appropriate solutions Develop desirable technologies Recover valuable nutrients from waste Produce consistent, high-value products Slide 3/20

5 Peri-Urban Case Study in Sub-Saharan Africa The sanitation deficit is largely regional with progress in Sub-Saharan Africa lagging behind Kanyama, Lusaka, Zambia Slide 4/20

6 Kanyama Compound Kanyama GIS MAP, Lusaka: formal (white) and peri-urban areas (grey), and centralized network (black lines) (Kennedy-Walker et al., 2015). Most populated of Lusaka s PUAs 250,000 low-income inhabitants Migrant workers renting No centralized sewage connections Large deficit in available pit latrines Annual flooding cholera & typhoid outbreaks Slide 5/20

7 FSM Challenges in Kanyama Roughly 95% of inhabitants use pit latrines. When pits are full 41% of households abandon it and build another, while 46% of households bury or dump the waste nearby. WSUP Baseline Survey, 2012 C. Rose C. Rose G. Collins The developing world has an opportunity to sidestep the costly and inefficient technologies widespread throughout the developed world and leapfrog to newer, more sustainable technologies Slide 6/20

8 User acceptability Perception Maintenance Technical Risk of hazardous components Pathogen kill Fit with existing system Management & administration Permanence Energy demand Construction material Life-cycle analysis Robustness Resource recovery Recovery Land use Water demand Environmental & system monitoring requirements Public health impacts & outcomes End-product reuse Employment opportunities Capital cost Soil & topography Climate Beliefs & values & values Local/national policy Socio-Cultural Trego et al. 2017, submitted User cost Slide 7/20

9 Anaerobic Digestion A Sustainable Process = the sequential, and co-operative, action of several groups of microorganisms underpinning breakdown of organics in the absence of oxygen Tes.com Nationalparks.gov NASA.gov Modernfarmer.com Sustainablog.org Slide 8/20

10 Transforming FSM in Kanyama Containment Pit latrines Treatment Phase 1: Fixed-dome digestion Biogas Collection Manual Transport Pushcarts One Product: Organic fertilizer Treatment Phase 2: Simple drying beds

11 Extracting Value From FSM Treatment Containment Pit latrines Treatment Phase 1: Fixed-dome digestion Biogas Collection Manual Transport Pushcarts Sludge Cake (P) Blend (N:P) Material (N) Treatment Phase 2: Modified drying beds for N & P recovery

12 Lab-Scale Trial INFLUENT CH 4 DIGESTATE Phase 2 - MODIFIED DRYING BEDS: dewater anaerobic digestate & recover N & P Phase 1 - DIGESTER: reduce solids content & produce biogas EFFLUENT

13 Sequencing Batch Reactor 20-L working volume; 37 C INFLUENT CH 4 Descending baffle to retain new influent Effluent displaced during feeding Inoculated with cattle slurry 1:1 ratio based on VS Sequencing batch mode Fed manually every 3 rd day 30-day retention time Intermittently mixed External mechanical mixer & descending rod 8 times per day for 5-minute durations Slide 12/20

14 Solids (%) Digester Performance Solids Destruction 6,5 6 5,5 5 4,5 4 3, Time (d) Effluent TS Influent TS Effluent VS Influent VS reduction in total and volatile solids (TS & VS) ammonification: 100 mg/l 500 mg/l Slide 13/20

15 Volume Biogas (L) Methane (%) Digester Performance Biogas Production Time (d) Cumulative Volume of Biogas % Methane Cumulative production of biogas Increasing CH 4 concentration over time Slide 14/20

16 Summary Digester Performance 17% reduction in TS & VS Average concentration of 55% CH 4 yield of 0.88 L CH 4 /gvs removed First retention time: reduction in total and volatile solids (TS & VS) release of soluble COD Cumulative production of biogas Increasing CH 4 concentration over time Slide 15/20

17 Lab-Scale Dynamic Column Experiments Phase 2 - MODIFIED DRYING BEDS: dewater anaerobic digestate & recover N & P flow rates ammonium concentration size & type of material Slide 16/20

18 Modified Sludge Drying Bed Design DIGESTATE Sacrificial Sand Layer to prevent clogging Packing density: 1.8 g/cm 3 Bed depth: 50 mm Particle size: 1.5 mm Clinoptilolite Layer for NH 4 + recovery Packing density: 0.75 g/cm 3 Bed depth: 220 mm Particle size: 2-4 mm DRYING BED EFFLUENT Gravel Layer to enable drainage Packing density: 1.75 g/cm 3 Bed depth: 50 mm Particle size: 6 mm Slide 17/20

19 Clinoptilolite Zeolite Highly porous Low-cost Can be directly applied as a fertilizer Ammonium Affinity Cation exchange Selectivity sequence: K + >NH 4+ >Na + >Ca 2+ Good Performance 62-99% removal despite high solids loading Capacity of 60 g NH 4 -N/kg clinoptilolite Provides fertilizer product grade 5.9 wt.% NH 4 -N

20 Potential Flow Sheet for Sustainable PUA FSM Slide 19/20

21 Outlook Path Forward POSITIVE: Developing nations are in unique positions to implement sustainable sanitation technologies, and AD has clear potential Revenue from recovery of valuable end-products can underwrite less lucrative stages of FSM Modified sludge drying beds are feasible for recovery of key macro-nutrients (N, P, K) required in agriculture. Clinoptilolite has great potential as a non-regenerative medium for drying-beds Slide 20/20

22 Thank you for listening! Anna Trego National University of Ireland Galway Dr. Gavin Collins National University of Ireland Galway