Surahammar: a case study of the impacts of installing food waste disposers in 50% of households

Abstract

This paper reviews 15 years of sewage works' monitoring data to assess the effect of installing in-sink food waste disposers (FWD) and how these effects compare with the published scientific literature. For the first time, it has been possible to assess at full scale the load/cost transfer from solid-waste to wastewater management. Within a period of 10 years, 50% of households in the town of Surahammar in Sweden chose to have FWD installed as their means of managing their kitchen food waste. The drainage from the households feeds a single wastewater treatment works (WwTW) that comprises primary settlement, activated sludge, followed by chemical phosphate precipitation and mesophilic anaerobic digestion. The sewer system is separate but with overflow between foul and surface water in times of surcharge; the diameters and gradients of the sewers are unexceptional. This paper reviews the influent and biogas monitoring data for the 2 1 2 years before installation started and the 10 years after the first peak of installations (by which time they had been installed in 30% of households). This provides a unique opportunity to verify the published research on FWD. The operational monitoring data are consistent with the already published research that FWD have little or no impact on water use, sewer blockages, vermin or wastewater treatment. The data are consistent with a hypothesis that in-sewer biological process acclimated to the change in wastewater composition and treated the dissolved and fine particulate load before it reached the WwTW. The digesters produced 46% more biogas than before FWD were installed (P =0.01). There was no significant increase in hydraulic load, or in the loading of BOD 7 , COD, N or NH 4 . As a result of Surahammar's overall waste strategy, not just the FWD, but the tonnage of waste to landfill from the municipality has also decreased from 3600 tonnes/ year in 1996 to 1400 tonnes/year in 2007.

Decentralised schemes for integrated management of wastewater and domestic organic waste: the case of a small community

“…Schemes A2 and B2 include the integration of FWDs in 50% of the households of the community. Both electricity and tap water are supplied to pump the combined stream of wastewater and DOW to the WWTP (Evans et al, 2010). Primary settling is applied after screening to separate the primary sludge from the primary effluent.…”

Spatial and temporal variability of bacterial communities within a combined sewer system

“…Measurements of biological oxygen demand (BOD5) in the inlet of a wastewater treatment plant by Evans et al. () implied temporal variability in the inlet wastewater composition; however, changes in the microbial communities that are present within the supplying sewer network have seldom been investigated. The variable conditions in sewers, whether chemical or physical, can affect microbial communities in several ways.…”

“…Vollertsen et al (2005) showed large spatial variability in chemical oxygen demand (COD) fractionation of the organic matter in 109 wastewater samples collected from five different in-sewer locations in north Denmark. Measurements of biological oxygen demand (BOD5) in the inlet of a wastewater treatment plant by Evans et al (2010) implied temporal variability in the inlet wastewater composition; however, changes in the microbial communities that are present within the supplying sewer network have seldom been investigated. The variable conditions in sewers, whether chemical or physical, can affect microbial communities in several ways.…”

Domestic food waste – the carbon and financial costs of the options

“…It went on to assume for the purpose of predicting impact on water resources that there would be an increase of 1 US gallon per person per day but this seems to have been arbitrary and unconnected with the actual measurements made in the field study (New York City DEP, 1999). Evans et al (2010) found the flow into a wastewater treatment works (WwTW) did not change significantly between the time when there were no FWDs and when 50% of the 3700 households used FWDs.…”

“…Surahammar in Sweden provided Evans et al (2010) with an opportunity to assess the cost transfer from solid waste to wastewater, because in the space of 12 years FWD installation changed from 0% to 50% of households and throughout this period the WwTW that serves the municipality collected and analysed 4-weekly, 24-hour composite samples of the influent. The sewerage is largely separate surface and sanitary sewers with interconnection to relieve excess flow.…”