Effect of Organic Loading Rate on Aerobic Granulation. I: Reactor Performance

• Published in: Journal of environmental engineering (New York, N.Y.) Vol. 130; no. 10; pp. 1094 - 1101
• Main Authors: Tay, Joo-Hwa, Pan, Shun, He, Yanxin, Tay, Stephen Tiong Lee
• Format: Journal Article
• Language: English
• Published: Reston, VA American Society of Civil Engineers 01.10.2004
• Subjects: Applied sciences; Biological and medical sciences; Biological treatment of waters; Biotechnology; Environment and pollution; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General purification processes; Industrial applications and implications. Economical aspects; Pollution; TECHNICAL PAPERS; Wastewaters; Water treatment and pollution; Biodegradation; Bioreactor; Granulation; Organic loading; Sequential aerobic sludge blanket reactor; Aerobe; Waste water purification; Performance; Biological purification
• ISSN: 0733-9372; 1943-7870
• DOI: 10.1061/(ASCE)0733-9372(2004)130:10(1094)

The effect of organic loading rate (OLR) on the aerobic granulation process was investigated using laboratory-scale sequential aerobic sludge blanket reactors (SASBRs). Reactors R1, R2, R3, and R4 were operated at OLRs of 1, 2, 4 and 8kg chemical oxygen demand (COD)/m3day, respectively. Aerobic granules could not be formed at the relatively low OLRs in R1 and R2. Stable aerobic granules were successfully cultivated at the mid-range OLR of 4kg COD/m3day tested in Reactor R3. These granules first appeared 14 days after startup and eventually grew to become the dominant form of biomass in R3. The granular biomass stabilized at a mixed liquor volatile suspended solids (MLVSS) concentration of 12,000mg/L, with a food-to-microorganism (F/M) ratio of 0.33kg COD/kg MLVSSday and a mean cell residence time of 31.1 days. Aerobic granules were first observed on Day 18 in Reactor R4, which operated at the highest OLR tested of 8kg COD/m3day. However, these granules were unstable and eventually washed out of R4. The best reactor performance was achieved in R3 with a COD removal rate of 99%, an observed yield coefficient (YOB) of 0.10mg MLVSS/mg COD, and a sludge volume index 24mL/g MLVSS. The volumetric specific oxygen utilization rate was highest in R3, at 356mg O2/Lh. An optimal choice of OLR was found to favor the cultivation and retention of well-settling granules and enhanced the overall ability of the reactor to remove COD. This study contributes to a better understanding of the role of OLR in aerobic granulation.