Enhancement of Hydrogen and Methane Production by Ultrasonication of Municipal Sludge

Abstract

This work successfully investigated biohydrogen, biomethane and volatile fatty acids production from different organic rich waste materials under different operational conditions. Waste activated sludge and sedimented fibres have been used as substrates for the anaerobic digestion process. Glucose has been used as a model compound. The impact of different operational conditions such as pretreatment technologies, pH, temperature, mode of operation (batch; continuous) and one stage anaerobic digestion vs. two stage anaerobic digestion has been investigated. Two inocula were used for hydrogen and methane production. Pretreated activated sludge for hydrogen production and digested sludge for methane production. Activated sludge process is the most applied wastewater treatment technology in Egypt. As a result of population increase, industrial development, increasing coverage with wastewater treatment facilities, sludge production in Egypt is rapidly increasing. Sewage sludge is the semi-solid material which results from wastewater treatment process, generally classified as hazardous waste due to its high content of various bacterial species, pathogenic microorganisms, nitrogen, phosphorus, organic and inorganic micropollutants. Pulp and paper industry consumes huge amounts of fresh water and discharge wastewater containing high concentrations of sludge. For decades, pulp and paper wastewater was discharged into the nearby water bodies without any treatment which resulted in the accumulation of fibres on the bottom of the receiving water bodies. Sludge accumulated on the bottom of Lake Näsijärvi (Tampere, Finland) as a result of discharge of untreated pulp and paper wastewater (1.5 x106 m3) is the subject of the present study for biogas production via anaerobic treatment.

5.1. Hydrogen production from glucose Start-up and selection of a suitable microbial community is a crucial phase in dark fermentation process. Acid-heat pretreated fresh activated sludge was used as inocula, in four consecutive batch cycles, for H2 production from glucose at 37°C. Acid-heat pretreatment was very effective in harvesting the hydrogen producing species and destroyed the other competitors or consumers. No methane was determined during the four batch cultures. This inoculum achieved hydrogen yield of 1.7 mol H2/mol glucose. Acetate, butyrate and propionate were the main metabolites produced from the dark fermentation of glucose. The hydrogen consumption was accompanied by an increasing concentration of acetate suggesting hydrogen consumption by homoacetogensis.