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Quantifying the power of in-sewer treatment

Quantifying the power of in-sewer treatment. Tim Evans *, Maria Sandell **, Per Andersson** and Åsa Wievegg** * Tim Evans environment , Stonecroft, Park Lane, Ashtead, KT21 1EU, UK tim@timevansenvironment.com ** Surahammars KommunalTeknik AB, Box 10, 735 21 Surahammar, Sweden.

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Quantifying the power of in-sewer treatment

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  1. Quantifying the power of in-sewer treatment Tim Evans*, Maria Sandell**, Per Andersson** and Åsa Wievegg** * Tim Evans environment, Stonecroft, Park Lane, Ashtead, KT21 1EU, UK tim@timevansenvironment.com ** SurahammarsKommunalTeknik AB, Box 10, 735 21 Surahammar, Sweden SPN7 2013 7th International Conference on Sewer Processes & Networks, 28 - 30 August 2013, Sheffield

  2. Proposition • In 1997 Surahammar offered citizens food waste disposers as an option • By 2008 50% of households used them • Number of citizens and households had not changed • The amount of biodegradable matter discharged to sewer must have increased • WwTW influent monitored systematically: • 24-hour composite samples taken 4-weekly • Mass balance of what went in compared with what arrived at WwTW must be what bio-transformed in the sewers [if it didn’t settle out] • Jonathan Mattsson and AnnelieHedström are the latest, and most comprehensive, to show it does not settle

  3. Surahammar: founded 16th and 17th centuries based on iron. Birthplace of Swedish car industry (1897) Topography: gently rolling Approx 10100 people living in 3700 households Sewers separate with interconnection weirs – sewers laid at 0.004-0.005; Haga WwTW: primary settlement – activated sludge – mesophilic anaerobic digestion – sludge to drying beds – Miscanthus grass – topsoil manufacture

  4. ≈ 1500 people ≈ 1500 people ≈ 7100 people Haga WwTW

  5. Surahammar Kommunal Teknik AB (SKT) • 1993 pre-study of FWD • 32 apartments with FWD + 7 without • sewers - no effect; residents - 96% satisfied; water consumption 25% less[?]; refuse 4.8m3 to 1.2m3 /week • 1997 launched new waste charges • Home composting = £0 • 8-year lease FWD from SKT = £27/year • Kerbside separate collection = £209/year • Central drop-off bins for card, paper, plastic, glass, metal • By 1998 30% of households (1110) were leasing FWD • By 2008 50% of households (1850) were leasing FWD • Total waste to landfill 1996 = 3600t - in 2007 = 1400t

  6. Secondary [biological] treatment [of ‘settled sewage’] Influent sample point24 hour composite4-weekly 92% on Wednesdays 3mm screens Reclaimed water Primary treatment/settlement Grit settlement Final settlement/ clarification Screenings and grit to disposal ‘return’ or ‘surplus’ activated sludge or ‘humus’ sludge in the case of biological filters Storm tanks(to balance excess flow) Sludge digestion Samples analysed used Swedish Standards methods

  7. What are FWD inputting?Kegebein, J.; Hoffmann, E. and Hahn, H.H. (2001) Co-Transport and Co-Reuse, An Alternative to Separate Bio-Waste Collection? Wasser. Abwasser 142, 429-434 Sieve analysis – 2 samples • 15% - 36% “dissolved” • 98% <2mm • 100% <5mm • Sediment-free transport at 0.1m/sec Settling velocity m/h

  8. Estimates of the contributions made by FWD to wastewater composition based on laboratory studies

  9. Estimates of the effect of FWD based on samples taken from sewers, from pumping stations or from a WwTW Greatest difference closest to kitchens and least difference furthest from kitchens and longest time for acclimation

  10. Daily flow of influent (m3/day) measured after 3mm screens and grit settlement at the time of 4‑weekly sample collection data point for 10 January 2001, 19813 m3/day omitted

  11. BOD7 loading (kgBOD7/day) - 4 weekly 24-hour composites extreme data points omitted: 16/10/96 1117 kgBOD/d; 08/03/00 1166 kgBOD/d; 10/01/01 1446 kgBOD/d

  12. Mean 484 Mean 410 Mean 331 Average annual biogas (m3/day)[1995, 1996, 1997 and 1998 are from Karlberg & Norin, 1999]

  13. Student's t-test comparing influent and biogas pre and post FWD installation (from Evans et al., 2010) Analytical suite did not include SS unfortunately

  14. Estimates of the effect of FWD based on samples taken from sewers, from pumping stations or from a WwTW BOD:N 4.6 1.8 7.0 3.2

  15. Conclusions • We know 50% of households use FWD to divert kitchen food waste to sewer • Surahammar+Ramnäs discharges to Haga ≈ 8600 people • Extra input from averages of lab studies x 8600 x 50%124kg BOD/d; 251 kg COD/d and 6.5kg N/d • Influent monitoring at Haga 0% FWD minus 50% FWD-67kg BOD/d (P 0.06); -192 kg COD/d (P 0.09) and -7kg N/d (P 0.18) • Mass balance: sewer biofilms bio-transformed191kg BOD/d; 443 kg COD/d and 13.5kg N/d44 g BOD/cap.d; 103 gCOD/cap.dand 3.1gN/cap.d for each person in a FWD household • Has biofilm ecology changed? tim@timevansenvironment.com

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