Control of sludge bulking in an SBR - plant treating slaughterhouse wastewater

Control of sludge bulking in an SBR-plant treating slaughterhouse wastewater Linda Jonsson In December 2003 the new plant treating slaughterhouse wastewater from KLS was taken into operation. Läckeby Water Group was entrepreneur and responsible for the maintenance during the following two years. The treatment plant is of SBR-type and has biological nitrate removal and chemical precipitation of phosphate with iron chloride. The wastewater from the slaughterhouse passes a 2 km long pipeline before entering the treatment plant. During 2004, the plant had problems with high levels of phosphorous in the effluent, several mechanical problems and two occasions of sludge bulking caused by filamentous bacteria. The first incident was caused by Thiothrix spp. and the second by Type 021N. The aim with the thesis was to find causes for the latest period of sludge bulking as well as investigate preparatory actions against Type 021N. The thesis included literature studies, laboratory and full-scale tests, evaluation of prior process data and continuous microscopic analysis of the activated sludge at the plant. The literature study showed that filamentous bacteria are favoured by low oxygen and low nutrient concentrations due to their possibly higher growth rate during low substrate concentrations. Type 021N, specifically, can use reduced sulphides as energy source and benefits from an excess of low molecular substrates. Laboratory experiments did not verify that the filamentous bacteria were favoured by low oxygen concentration or low phosphate levels. The effect of FeCl 3 , Ecofloc, PAX-XL60, NaOCl and H 2 O 2 added to a bulking sludge was evaluated by microscopic analysis. No chemical was found to suppress the filamentous bacteria without also affecting the floc-forming bacteria negatively. PAX-XL60 showed the largest negative effects on filamentous bacteria and only a minor impact on other microorganisms. Full-scale tests with PAX were thereafter performed in order to suppress filamentous bacteria as well as flocculate particulate solids. The effect of earlier additions of NaOCl and H 2 O 2 into the process gave varied results. NaOCl was efficient against filamentous bacteria when addition was made during correct circumstances. Process data from two separate periods during 2004 was compared. One period was followed by good effluent values and another period by a sludge bulking period. Large differences between the two periods were seen in oxygen conditions, temperature, FeCl 3 dosage and organic load. Measurements on influent wastewater showed high levels of hydrogen sulphide, which can be produced during anaerobe …