SLUDGE-GROWN ALGAE FOR CULTURING AQUATIC ORGANISMS .1. ALGAL GROWTH IN SLUDGE EXTRACTS

This project is aimed al studying the feasibility of using sewage slud ge to prepare culture media for microalgae (Chlorella-HKBU) and the us e of the sludge-grown algae as a feed for some aquatic organisms. Part I of the project included results on preparing sludge extracts and th eir use on algal culture. By comparing two culturing techniques, ''aer ation'' and ''shaking,'' ii was noted that both lag and log phases wer e shortened in the aeration system. A subsequent experiment noted that algal growth subject to aeration rates of 1.0 and 1.5 liters/min had similar lag and log phases. in addition, both aeration rates had a sig nificantly higher (P < 0.05) final cell density than that of 0.5 liter s/min. A detailed study on the variation oi growth conditions on the a lgal growth was done. The results indicated that pH values of ail the cultures declined below 5 at day 12. The removal rates of ammonia N ra nged from 62% to 70%. The sludge-grown algae contained a rather substa ntial amount of heavy metals (mu g/g): Zn 289-581, Cu 443-682, Ni 310- 963, Mn 96-126, Cr 25-118, and Fe 438-653. This implied that the rathe r high levels oi heavy metals may impose adverse effects an higher tro phic organisms.