Anaerobic co-digestion of food waste and FOG with sewage sludge – realising its potential in Ireland

Abstract

The severe environmental pollution in many countries is caused by indiscriminate discharge of large quantities of food waste (FW), fat oil and grease (FOG) and sewage sludge (SS) to the environment. There are many possible treatment routes, but anaerobic digestion (AD) is now well accepted for treating several kinds of organic wastes. But AD of FW alone presents some operational challenges because of substrates and variability. Anaerobic co-digestion of two or more substrates is better than single substrate digestion. This can use a plant’s unused capacity, in line with the trend to renewable energy. Co-digestion technology, although well established in many European countries, is still in its infancy in Ireland. There are problems with different regulatory arrangements. They should be resolved. The paper reviews anaerobic co-digestion technology is reviewed, with special focus on possible application in Ireland.

Keywords:

• FW
• sludge
• co-digestion
• FOG
• biogas
• biodegradability

Abbreviations:

• ABP, anaerobic by-products
• AD, anaerobic digestion
• AS, activated sludge
• ASBR, anaerobic sequential batch reactor
• BMW, biodegradable municipal solid waste
• BMP, bio-methane potential
• BNR, biological nutrient removal
• BOD, biochemical oxygen demand
• CGY, crude glycerine
• CH₄, methane
• C/N, carbon nitrogen ratio
• COD, chemical oxygen demand
• CO₂, carbon dioxide
• CSTR, continuous stirred tank reactor
• DM, dissolved matter
• DS, dissolved solids
• FFA, free fatty acid
• FOG, fat, oil and grease
• FVW, fruit vegetable waste
• FW, food waste
• GHGs, greenhouse gases
• GW, grease waste
• HRT, hydraulic retention time
• LCFAs, long chain fatty acids
• MSW, municipal solid waste
• -N, ammonium nitrogen
• NH₃, ammonia
• OFMSW, organic fraction of municipal solid waste
• OLR, organic loading rate
• PE, population equivalent
• PS, primary sludge
• SBR, sequencing batch reactor
• SMP, specific methane potential
• SRT, sludge retention time
• SS, sewage sludge
• T, temperature
• TPAD, two-phase anaerobic digestion
• TS, total solids
• TSS, total suspended solids
• UASB, upflow anaerobic sludge blanket
• VFA, volatile fatty acid
• VS, volatile solids
• VSS, volatile suspended solids
• WAS, waste activated sludge
• WWTPs, wastewater treatment plants

Acknowledgement

The first author acknowledges the support from the Civil Engineering Department of University College Dublin, scholarship support from Student Universal Support Ireland (SUSI) and Université de Toulouse, Mines Albi, CNRS UMR 5302, Centre RAPSODEE, Campus Jarlard, Albi, F-81013 cedex 09, France.