The rising of human population in the world leads to the increasing number of food waste annually. To counter this problem, the food waste is suggested to be recycled into value-added product. Anaerobic digestion is one of the ways to recycle the food waste. The main product of a complete anaerobic digestion is methane (biogas). However, methane is very hard to handle since it is in gas form. Hence, this paper has drawn the attention toward the intermediate product of anaerobic digestion, the lactic acid. This paper presents the effect of 3 different variables: (a) pH values, (b) temperature and (c) amount of inoculum, on the hydrolysis and acidogenesis stages of anaerobic digestion of food waste. Besides, the optimal condition was determined. Experimental results show that the optimum, 0.0845 g/mL of lactic acid was obtained at pH value of 7, with 125 g of volatile solid food waste and 100 g of inoculum (Ragi Tapai), and was left in a pre-heated oven at 45°C for four days. This value was higher than the other previous study, and so showing promise in producing green acid from food waste that can be used as an intermediate substance for making other materials.

The amount of alum sludge produced at water treatment plant has become a problem where it is highly costly in order to dispose them. Various research was conducted to find the most suitable and economic alternative to recycle and reused of alum sludge. In this study, alum sludge was retrieved from Waterworks where it was dewatered, dried, grounded and sieved to obtain smallest particle sizes of alum sludge. The synthetic water was prepared at the laboratory in as it was used to imitate the properties of real water contaminated with chromium. This study was conducted to determine the percentage reduction of chromium concentration in synthetic water by using alum sludge as absorbent. The percentage reduction of chromium was observed under the effect of initial concentration of chromium and the height of alum sludge. The result indicates that chromium concentration reduction was the highest at the lowest initial concentration and at the highest height of alum sludge and vice versa.