Kitchen garbage generated at a school cafeteria was treated and stabilised in a controlled on-site composting unit for volume reduction and on-site utilisation of processed garbage. The on-site composter was fed with the garbage on a daily basis during the two-months experimental period. Compost was not removed from the unit but was entirely reused as a bulking agent in order to minimise the need for additional bulking agent and compost handling. Performance of the composter tinder this condition was investigated. Most of the easily degradable organic matter (EDM) in the garbage was biodegraded rapidly, and the final product had a low content of EDM. Lipids, total sugar, and hemi-cellulose were degraded 96%, 81%, and 66% respectively. Free air space (FAS) was higher than 0.5 all the time, so accumulation of dry matter in the unit was not significant in reducing reaction efficiency. Other reaction parameters such as pH and MC were kept within a suitable range; however, it was advisable to maintain MC at over 46%. As a result, this method of operation was able to stabilise the garbage with low sawdust demand and little compost production.
Various sludge concentrations and aeration rates were evaluated to find the optimal operation condition of a submerged ceramic membrane filtration system. 5.6 g/L of sludge was diluted with water to concentrations of 2.8 g/L and 1.4 g/L, and the three sludge concentrations were compared in terms of titration characteristics such as pressure and filtrate flux. Flux was at the highest value of about 30 L/m2 x hr at 50 kPa when sludge concentration was 1.4 g/L. In contrast, when sludge concentrations increased to 2.8 g/L and 5.6 g/L, the flux at 50 kPa decreased significantly to 18 L/m2 x hr and 10 L/m2 x hr, respectively. It was concluded that the sludge concentration directly affected the filtration efficiency, and low sludge concentration was suitable for improving filtration efficiency. Adjusting the aeration rate from 2 L/min to 4 L/min at 5.6 g/L of sludge and 50 kPa of pressure increased flux from 10 L/m2 x hr to 13 L/m2 x hr. It was obvious that the vigorous aeration improved the filtration efficiency, but the aeration rate did not seem to be high enough to maintain flux lower than critical flux.
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