Monitoring process efficiency of a full-scale in-vessel system for composting fisheries wastes

This study, which used data obtained from samples from a full-scale fish waste composting facility, examined the effect on the 'active' stage of composting when the weight ratio of bulking agent to fish was varied. Two weight ratios of bulking agent to fish wastes were tested experimentally (1:1 and 1.3:1). A monitoring strategy was adopted which used the concentrations of ammonia and volatile fatty acids as the major indices of the progress of the composting process. A headspace-gas chromatograph technique developed in the Bio-Resource Engineering laboratory was used to monitor the concentrations of volatile fatty acids. Both mixes satisfied the temperature requirements for the destruction of pathogens and, in both cases, total carbon declined gradually over the course of monitoring. A similar overall pattern was observed for both mixes in terms of a correlation between rises in temperature and increases in ammonia and volatile fatty acid production. However; a significant difference was recorded for the ammonia and volatile fatty acid concentrations of the two mixes, with higher concentrations recorded for the 1.3:1 mix in both cases. This indicated that while both mires composted well, the 1.3:1 mix did so more efficiently. Using the concentrations of ammonia and volatile fatty acids as major indices of the effectiveness of the active process proved to be a valuable monitoring strategy. The headspace analysis technique was a simple and effective method for determining the volatile fatty acid concentrations. Traditional indicators of moisture content, pH and temperature should also be monitored.