Control and optimization of wastewater treatment process in a paper manufacturing plant

Abstract

The objective of this study is to optimize a pulp and paper mill effluent treatment system through the control of filamentous foaming and bulking sludge. The investigation was carried out in three stages. The First stage of this work comprised of identification of the predominant filamentous microorganism that was responsible for the foaming and bulking problems in the activated sludge. Different diagnostic and examination methods were used in order to identify the particular microorganism found in the paper mill wastewater treatment plant. An actinmycetes, Nocardia amarae was identified to be the predominant filamentous species. In the second stage, the growth kinetics of the predominant filamentous microorganism and a non-filamentous floe-forming microbe were studied. The growth of filamentous N. amarae was favored by low food to microorganism (F/M) ratio, while growth of non-filamentous Pseduomonas aeruginosa was promoted by high F/M ratio. The cut-off F/M value that decided the predominant microbial species in competitive growth between filamentous and floe-forming bacteria was found at 0.52 mgBOD/mgMLSS/d. In the final stage of this research, a novel feast fast operation (FFO) was developed on the basis of the growth kinetics and inter-species interaction, to control the filamentous overgrowth and related foaming and bulking problems. Under FFO, the sludge microbes experienced repetitive switches between conditions of high and low F/M ratio during the course of wastewater treatment, thus avoided prolonged exposure of the sludge microbes to F/M ratio below 0.52 mgBOD/mgMLSS/d. The implementation of FFO showed quick response in suppression of filamentous growth as indicated by improved sludge settleability and reduced foaming in the system. Optimization of the FFO performance was achieved by proper control of the ratio of F/M loading between the feasting unit and the fasting unit within the system. The FFO was shown to be effective in improving the microbial population balance, sludge settleability and solving foaming problems without significant adverse effect on the process treatment performance and stability. In addition to findings on effluent treatment system, a new, convenient and reliable foam measurement method has been developed to diagnose the degree of foaming and the effectiveness of FFO.