Anaerobic co-digestion of municipal wastewater sludge with organic wastes

In municipal wastewater treatment plants, anaerobic digestion is applied for the treatment of sewage sludge. Digestion of sewage sludge produces a high level of alkalinity for buffering against pH variation; however, biogas production is limited due to the low organic content of the substrate. Anaerobic co-digestion is the simultaneous treatment of two or more organic waste streams such as sewage sludge and food waste. This process allows for the stabilisation of solid organic materials, whilst simultaneously providing a renewable source of energy in the form of biogas. Anaerobic co-digestion extends the scope of conventional anaerobic digestion by allowing for the treatment of substrates that are unsuitable for monodigestion. Substrates rich in inhibitory contaminants (such as sulphides, heavy metals or excess ammonia), readily degradable organics or deficient in buffering capacity can be paired with sewage sludge for stable operation and enhanced biogas production. Prior examples of co-substrates paired with sewage sludge include food waste, the organic fraction of municipal waste and slaughterhouse wastes. Ideal co-digestion pairings can also instigate a synergistic effect whereby degradation of both substrates is enhanced through the optimisation of reactor stoichiometry and biomass balance.