Biochemical methane potential of four species of Ulva and Gracilaria genus was assessed in batch assays at mesophilic temperature. The results indicate a higher specific methane production (per volatile solids) for one of the Ulva sp. compared with other macroalgae and for tests running with 2.5% of total solids (196±9 L CH(4) kg(-1)VS). Considering that macroalgae can potentially be a post treatment of municipal wastewater for nutrients removal, co-digestion of macroalgae with waste activated sludge (WAS) was assessed. The co-digestion of macroalgae (15%) with WAS (85%) is feasible at a rate of methane production 26% higher than WAS alone without decreasing the overall biodegradability of the substrate (42-45% methane yield). The use of anoxic marine sediment as inoculum had no positive effect on the methane production in batch assays. The limiting step of the overall anaerobic digestion process was the hydrolysis.

The biochemical methane potential (BMP) of raw poultry litter waste was assessed in batch assays. Biological co-treatment with Clostridium cellulolyticum, Caldicellulosiruptor saccharolyticum and Clostridium thermocellum as bioaugmentation strains, and thermochemical pre-treatments with lime and sodium hydroxide performed at different temperatures and pressures were applied as strategies to improve the BMP by favouring the hydrolysis of the cellulolytic material in the waste. Anaerobic digestion of the raw waste allowed a specific methane production of 145 ± 14 LCH(4)kg(-1)VS, with 1% total solids and 0.72 g VS(inoculum)g(-1)VS(waste). The pre- and co-treatments contributed to a significant increase (up to 74%) in the waste solubilisation when using C. saccharolyticum, but methane production did not improve considerably. Therefore, the conversion of soluble organic matter to methane was the limiting step of the anaerobic digestion process of poultry litter waste.

Manufacturing processes in fish canning industries generate a considerable amount of solid waste that can be digested anaerobically. The aim of this research was to study the biochemical methane potential of different solid fish waste. For tuna, sardine and needle fish waste, around 0.47g COD-CH(4)/g COD(added) was obtained in batch experiments with 1%TS; whereas for mackerel waste, the methane production attained 0.59g COD-CH(4)/g COD(added). The increase in the waste/inoculum ratio, from 1.1-1.3 to 2.8-3.3g VS(waste)/g VS(inoculum), led to overload due to VFA and LCFA accumulation. Afterward, co-digestion assays of fish waste with gorse were undertaken but the biochemical methane potential did not improve.