New biofouling prevention concepts tested and knowledge about of nano scaled silver in water circuits of paper industries
Sustainable water use in chemical, paper, textile and food industries
Microbial growth is an important topic in industrial water systems. Problems like the formation of biofouling on pipes and membranes reduce the performances of the systems and microbiological pollutants limit the use of water. Prevention technologies like Denutritor and Nanosilver decrease the use of chemicals for water conditioning and cleaning, and increase the possibilities of water recycling and re-use. This report describes laboratory tests to evaluate the potential of the use of Denutritor for biofouling reduction and microbial growth in waste water from the chemical industry and rain water for application in food industries, and tests to evaluate the impact of Ag nanoparticles on biological processes in effluent treatment for the paper industry. Denutritor pilot tests in chemical and food industry were started (WP 5.2 and WP 5.3) based on the results of these laboratory tests. Perstorp Specialty Chemicals, Sweden, intends to re-use effluent from their activated sludge Waste Water Treatment Plant (WWTP) for cooling and other industrial applications. For re-use, biofouling potential and salts concentrations of the WWTP effluent must be reduced. In laboratory tests with synthetic Perstorp WWTP effluent it is demonstrated, that Denutritor can be used to reduce the biofouling potential of this water type. An about 8-fold reduction appears to be within reach. Unilever Ben&Jerry’s Factory in The Netherlands is aiming to re-use collected rainwater for cleaning of packing and transport material. However, rainwater can contain a relatively high concentration of (pathogenic) micro organisms, which should be removed before the water can be used for these types of application in the food-sector. Laboratory tests with collected and recirculated rainwater showed that Denutritor can reduce coliforms, E. coli and pathogenic bacteria present in collected rainwater, but not remove them all. The amount of viable bacteria can additionally be reduced with 90-99% efficiency by exposure to UV doses between 50 and 2500 J/L, to further prevent the downstream process water for application in food industry. During these laboratory tests, three new types of biofouling monitors were evaluated for use in the on-site Denutritor pilot trials at Perstorp (WP 5.2) and at Unilever, Hellendoorn (WP 5.3). The biofouling monitors were exposed to Denutritor influent and effluent water, to allow the growth of microbial biofilms (biofouling) on their surfaces. The increase of protein concentration on the monitors appeared to be a good indicator of the biofouling potential of the synthetic WWTP effluent water tested. Biofouling monitors made from silicon or polyethylene (PE) tubes worked fine and were finally selected for use during the Denutritor pilots. The effect of silver nanoparticles has been analysed using model systems for anaerobic and aerobic treatment processes. The impact of nanoscale silver on the respiratory activity of aerobic activated sludge was traced continuously by means of respirometric measurement. Industrial process media (effluents, activated sludge, pellet sludge) from a paper mill were used for the analyses. Furthermore, trials were conducted in lab-scale at PTS and on mill-site to study the action that surface-bonded Ag nanoparticles had on preventing slime formation. It was found in model experiments on anaerobic and aerobic biodegradability that concentrations of nanoscale silver <30 mg/l did not cause any impairment of these processes. Contents above this value, however, reduced process efficiency.