This study compares the potential environmental impacts of various upgrade options on a wastewater treatment plant in Istanbul. The scenario of adding food waste to the wastewater, via food waste disposers, had the best performance in terms of climate change, terrestrial acidification, terrestrial ecotoxicity and fossil depletion.

Abstract: Life cycle assessment (LCA) is a beneficial tool to evaluate the performance of wastewater treatment plants (WWTPs) and to compare different upgrading options. The main objective of this study is to investigate the environmental impact of upgrading options of a preliminary WWTP in Istanbul, Turkey. The preliminary plant currently consists of mechanical treatment units and various upgrading options including primary treatment and high-rate activated sludge system (HRAS) process as well as the addition of food waste to wastewater were compared. Results showed that the baseline scenario (S0) had worse performance than all future scenarios (S1-3) except for climate change. The scenario of adding food waste to wastewater (S3) has the best performance in climate change, terrestrial acidification, terrestrial ecotoxicity and fossil depletion. Increased addition of food waste was also tested in the sensitivity analysis, and major improvements were obtained especially in climate change and terrestrial ecotoxicity.

Source: Huseyin Guven, Ola Eriksson, Zhao Wang, Izzet Ozturk (2018) Life cycle assessment of upgrading options of a preliminary wastewater treatment plant including food waste addition

This programme, funded by the Engineering and Physical Sciences Research Council (EPSRC), has developed a novel modelling approach to predict transport and settling of ground food waste particles emitted by FWDs into sewers.  The work is showing that fears of blockages are unfounded.  The current phase is examining the transformation of these particles as they pass through the sewer system and their potential contribution to biogas recovery. 

Source: Legge, Abigail & Jensen, Henriette & Tait, Simon & Nichols, Andy & Ashley, Richard. (2018). Modelling of Food Waste Disposer particle transport through a sewer network.

This study concludes that if carefully applied, co-digestion (of food waste and sewage sludge) can deliver beneficial synergies for the water industry and authorities responsible for food waste management. It proposes that all relevant stakeholders and regulators, should support changes to current regulatory frameworks to open a way forward for co-digestion in Ireland.

Source: Olumide Wesley Awe, Yaqian Zhao, Ange Nzihou, Doan Pham Minh (2017): Anaerobic co-digestion of food waste and FOG with sewage sludge – realising its potential in Ireland

This study revealed that integrating FWDs in a developing economy with a high fraction of food waste can be a viable alternative solution.The results indicated that adopting a FWD policy reduced emissions by about 42% at potential cost savings of 28%.

Source: Maalouf, Amani & El-Fadel, Mutasem. (2017). Effect of a food waste disposer policy on solid waste and wastewater management with economic implications of environmental externalities. Waste Management. 69. 10.1016/j.wasman.2017.08.008.

This study looked at five urban systems for collection, transport, treatment and nutrient recovery from blackwater, greywater and food waste, using data from Sweden and northern Europe. It showed that source control systems have the potential to increase biogas production by more than 70% compared to a conventional system and give a high recovery of phosphorus and nitrogen and biofertilizer.

(Abstract: In the last decades, the focus on waste and wastewater treatment systems has shifted towards increased recovery of energy and nutrients. Separation of urban food waste (FW) and domestic wastewaters using source control systems could aid this increase; however, their effect on overall sustainability is unknown. To obtain indicators for sustainability assessments, five urban systems for collection, transport, treatment and nutrient recovery from blackwater, greywater and FW were investigated using data from implementations in Sweden or northern Europe. The systems were evaluated against their potential for biogas production and nutrient recovery by the use of mass balances for organic material, nutrients and metals over the system components. The resulting indicators are presented in units suitable for use in future sustainability studies or life-cycle assessment of urban waste and wastewater systems. The indicators show that source control systems have the potential to increase biogas production by more than 70% compared with a conventional system and give a high recovery of phosphorus and nitrogen as biofertilizer. The total potential increase in gross energy equivalence for source control systems was 20-100%; the greatest increase shown is for vacuum-based systems.)

Source: H. Kjerstadius, S. Haghighatafshar & Å. Davidsson (2015) Potential for nutrient recovery and biogas production from blackwater, food waste and greywater in urban source control systems, Environmental Technology, 36:13, 1707-1720, DOI: 10.1080/09593330.2015.1007089

Recent report by Local Government Association (LGA) reviewed 147 pieces of literature available on food waste disposers (FWDs) in preparation for their forthcoming pilot study that will investigate the effects of domestic FWD usage in newly built homes. Out of 95 pieces of relevant research they found 60 that reported a positive impact from the use of FWDs. There were 23 pieces of primary research that  concluded FWDs have a positive impact on the environment and do not have a negative impact on the sewers or waste water treatment plants.  Key findings relating to the sewer network were:  most studies found there to be no clogging; evidence on sewage settlement indicated sewage with ground solids may ‘settle better’; anaerobic evidence pointed to increase in biogas production and enhancement of biological nutrient removal; and data on residual waste saw a fall in volume of the general refuse stream.

Source:

Roberts, P.; Davies, N. (October 2012) The potential of food waste disposal units to reduce costs – A literature review. Low and Behold Ltd.

Appendix

The Urban Water Research group at Luleå University of Technology has published a study showing that FWD has no significant long term impact on sewer system sedimentation. The study was carried out in 181 locations across almost 10km of pipes in the two municipalities of Surahammar and Smedjebacken, where FWDs were introduced on a larger scale more than a decade ago.

Source:

Mattsson,J.; Hedström, A. and Viklander, M. (2014) Long-term impacts on sewers following food waste disposer installation in housing areas– Environmental Technology, DOI: 10.1080/09593330.2014.915346

Desk study by a leading Danish engineering consultancy for members of the Danish Water and Wastewater Association and Danish municipalities. It contained previously undocumented operational experience from municipalities and made various positive conclusions. As a result of the study, Odense, Denmark’s third largest city, announced that it will permit FWD installations. Report concluded FWDs do not increase sedimentation and blockages and will not change the amount of fat in the sewer system. The extra water consumption is marginal and will not affect the hydraulic capacity of sewers or treatment plants. It also reported the amount of refuse is reduced by 20-30% with fewer odour problems, better hygiene for collection workers and possibility of less frequent collection.

Source:

Clauson-Kaas,J. and Kirkeby J. COWI (August 2011) Food waste disposers: energy, environmental and operational consequences of household residential use

After completing a comprehensive study on the impacts and benefits of food waste disposers, in September, 2008, the Stockholm Water Board voted to allow the installation of FWDs in all areas of their jurisdiction without prior approval, and also eliminated previously required surcharges. FWDs in Stockholm now play a major part in the national strategy to divert 35% of household food waste from incineration to biological recycling by 2010 (through biogas recapture in water plants).

Source:

Tendaj, M.; Snith, Å; von Scherling, M.; Hellström, M.; Mossakowska, A. and Millers-Dalsjö, D. (2008) Kitchen Disposal Units (KDU) in Stockholm. Stockholm Water's pre-study on the preconditions, options and consequences of introducing KDU in households in Stockholm. Stockholm Water

In a field trial that installed FWD in homes and a school for 67% of the 250 population of a mountain village in Italy the researchers found no problems in sewers, a benefit to wastewater treatment and a payback to the community of only 4-5 years.

Source:

Battistoni, P.; Fatone, F.; Passacantando, D.; Bolzonella, D. (2007) Application of food waste disposers and alternate cycles process in small-decentralized towns: A case study. Water Research. 41 893 – 903.

These UK counties have been subsidising the purchase of FWDs by residents since 2005, after studying the issue and concluding that using disposers was a cost-effective, convenient and hygienic means of diverting kitchen food waste from landfills. According to their analysis, using in-sink disposers for food waste costs less and has a better carbon footprint than other waste disposal options. The counties estimated that lower solid waste disposal costs would pay for the cost of subsidies in about three years.

Source:

Evans, T. D. (2007) Environmental impact study of food waste disposers for the County Surveyors’ Society & Herefordshire Council and Worcestershire County Council.

Study performed at request of Dutch government to analyse the effects on the Dutch sewer system from use of FWDs. Delft University of Technology conducted the study which concluded in July 2004. Conclusions were that the organic loading emanating from FWDs present negligible impacts to the sewer system or wastewater treatment facility.

Source:

de Koning, J. (July 2004) Environmental Aspects of Food Waste Disposers. Delft University of Technology.

Comprehensive four year study on the impact of disposers carried out in the town of Utanobori in Hokkaido. A technical report on the study found the installation of disposers did not result in any changes in the amount of system water usage; no large changes were evident in the amount of foreign material and deposits discharged at pump facilities; the frequency of cleaning did not change and no effects were observed to the quality of treated water. The popularisation of disposers would cause no changes to the environmental burden and an overall cost benefit analysis found that the convenience benefits and the cost of purchasing and installing a disposer to be an excellent value when compared to the changes in administrative costs and disposal operation costs.

Source:

Water Quality Control Dept., Sewage and Wastewater Management Dept, City and regional Development Bureau, Ministry of Land, Infrastructure and Transport, Japan Parks and Sewage Division, Department of Construction, Hokkaido Government, Town of Utanobori (2005) Report on Social Experiment of Garbage Grinder Introduction.

In 1998 The National Association of Heating, Plumbing, and Cooling Contractors commissioned a life-cycle comparison, at University of Wisconsin, of five engineered systems for managing food waste. The four-year research project concluded a FWD has the lowest cost to the municipality, the least air emissions, especially greenhouse gases and converts the food waste to a resource which may be recycled, making it the most environmentally friendly option for recycling biosolids.

Source:

Diggelmann, C.; Ham, R.K. (January 1998). Life-Cycle Comparison of Five Engineered Systems for Managing Food Waste.  Department of Civil and Environmental Engineering – University of Wisconsin. Waste Management & Research 21 501 – 514.

Research at the University of Karlsruhe in the department of Professor Herman H. Hahn, who for 11 years was the president of the German Water and Wastewater Association, demonstrates that the output of FWDs is transported through sewers easily. The study found that 40-50% of the output of a FWD was less than 0.5 mm and 98% was less than 2 mm by sieve analysis. All of the output passed a 5 mm sieve. Of the food waste sent down the FWD, between 15-36% of the output was dissolved. The output of the FWD was very finely divided and very biodegradable. They measured the density and settling velocities of bio-waste particles to be very much less than the mineral particles commonly found in sewer sediments.The study also found that FWD produces about 10 times more electricity (from the biogas) than the FWD uses.

Source:

Kegebein, J.; Hoffmann E.; Hahn H. (2001) Co- Transport and Co-Reuse – An Alternative to Separate Bio-Waste Collection?  Institute for Municipal Water Treatment, University of Karlsruhe. Wasser-Abwasser GWF 142 (2001) Nr. 6 429-434

In 2000 a comparative study of FWDs against other food waste solutions was carried out for Sydney apartment buildings, which at the time had the highest per capita installation of disposers. The impacts of FWDs in each area was compared to the impacts of the current practice of collecting food waste with municipal waste and sending it to landfill centralised composting of food and garden waste, and home composting. The report concluded the disposal of food with municipal waste was the least satisfactory of all options; individual composting was environmentally ideal but impractical for multi-unit dwellings. Using a food waste disposer was second best for energy consumption, global warming potential and acidification.

Source:

Wainberg, R.; Nielsen, J.; Lundie, S.; Peters, G.; Ashbolt, N.; Russell, D.; and Jankelson, C. (2000) Assessment of food disposal options in multi-unit dwellings in Sydney. CRC for Waste Management and Pollution Control Limited. Report 2883R.

Most recent piece of research, which has been accepted for publication in a peer reviewed journal, found FWDs contribute to increased production of sustainable energy, had no impact on the sewer system. To reduce waste sent to landfill the town of Surahammar offered its citizens differential charges for waste collection. This included home composting, kerbside collection and an 8-year contract to lease a food waste disposer (FWD) from Surahammar’s KommunalTeknik AB (SKT). Over the 10 years 50% of households chose the FWD option and it offered a unique chance to conduct a controlled study over a decade. This concluded there was no increase in water usage, sewer blockages, nor accumulation of solids, fat oil and grease, hydrogen sulphide or corrosion. There also was no change in wastewater treatment cost but on the contrary FWD usage increased biogas production by 46%.

Source:

Evans, T.D.; Andersson, P.; Wievegg, A.; Carlsson, I. (2010) Surahammar – a case study of the impacts of installing food waste disposers in fifty percent of households. Water Environment Journal, 241. 309-319.

In 1997 New York City rescinded its 18 year opposition to domestic FWDs, concluding that the opposition had no objective basis after a 21-month pilot proved their benefits exceeded any negligible impact on the sewer system and water quality. Among the issues examined were the impact of grease and food solids on sewers, the impact on water consumption and the impact of possible increased pollutant loading on receiving waters. The study concluded that the impact of food waste disposers in any of these areas was “de minimus.” The measure was signed into law by Mayor Giuliani in 1997.

Source:

www.nyc.gov/html/dep/pdf/grinders.pdf