After years of succesfull operation, the response of an anaerobic reactor changed completely. High caustic consumption was required, whereas PH remained on the low side; biogas flow rate had increased, but the calorific value was lower than usual. Granular anaerobic biomass was growing, but the net growth was washing out of the reactor.
After studying the results, it appeared that the changes coincided with a trial of a new type of biocide or slimicide. Although the biocide gave very good conditions for the paper machine, the effluent treatment plant developed several operational problems.
A solution was found by introducing small modifications, both in the mill as in the operation of the effluent treatment plant (ETP). After staff training in how to respond to the new situation, the ETP could be moved back on track again.