Control of filamentous organisms in food-processing wastewater treatment by intermittent aeration and selectors

Various measures were tested at a full-scale wastewater treatment plant to control sludge bulking by type 0041 and 0675 filamentous microorganisms, instigated by highly variable wastewater loadings from a food-processing facility. Intermittent aeration on a 1-h on 1-h off basis was found to effect a marginal improvement in sludge settling characteristics, as reflected by about an 11–36% reduction in the Sludge Volume Index (SVI) to 118 cm−3 g−1. At BOD loadings of 1500 kg d−1 which marginally exceeded the design capacity of the plant of 1200 kg d−1, SVI rose sharply to 230 cm−3 g−1 in less than a week. The anoxic selector effected a reduction in SVI to 170 cm−3 g−1 within 3 weeks of operation at temperatures of 8–12 °C. The aerobic selector was most effective, reducing SVIs further to 79 cm−3 g−1 in 2 weeks. Sludge settleablity was found to be inversely proportional to the aerobic selector food-to-microorganism ratio. The optimum aerobic selector loading was found to be 1.8–2.7 kgBOD5 kgMLVSS d−1, with corresponding SVIs in the range of 80–120 cm−3 g−1. © 2003 Society of Chemical Industry