Biocatalytic calcium removal from industrial wastewaters

Wastewaters having high calcium content; produce precipitates of different structure (as carbonate, sulfate or phosphate) in pipelines, boilers and heat exchangers and, affects adversely to aerobic and anaerobic reactors. As a remedy to this problem, the industry typically uses chemical crystallization reactors which are efficient but often require complex monitoring and control and, as a drawback, can give rise to highly alkaline effluents. Biomineralization are emerging as alternative mechanisms for the removal of Ca from aqueous environments. Bio-catalytic Calcification Reactors (BCR) utilize microbial urea hydrolysis by bacteria for the precipitation-removal of Ca, as calcite, from industrial wastewater. In this study, potential use of BCR for Ca removal from synthetic wastewater and real sugar wastewater were investigated. The main stages of this study were; (1) production of sludge which has ability to biocatalysing of Ca2+ removal in batch reactors, (2) determination of optimal conditions such as; time, pH value, urea, Ca, biomass, and organic matter concentrations, for effective Microbial Calcium Precipitation (MCP) (3) investigation of optimum design and operational parameters of BCR reactor in continuous feeding system, (4) determination of Ca effect on methanogenic microorganisms in UASB reactor, (5) researching of sequential BCR/UASB (Upflow Anaerobic Sludge Blanket) reactor system for treatment of Ca-rich wastewaters, (6) modification of CO2-stripper system with addition of BCR reactor installing in the recycle line at UASB treatment of Ca-rich wastewaters. In batch study, investigation of incubation time on Ca removal at synthetic wastewater where mineral medium and glucose-COD continuously refreshed, optimum incubation time was found as 6 days at these conditions. In batch study, investigation of urea effect on Ca removal, it was found that optimum urea concentration for effective Ca removal should be greater than Ca concentration required removal from water. In batch study, investigation of Ca concentration effect on Ca removal, removed Ca concentration was increased at samples containing higher Ca concentrations in synthetic wastewater with constant urea of 900 mg/L and varying Ca concentration between 0 and 2500 mg/L. In batch study, the investigation of initial pH of samples between 4-10 on calcium removal, calcium was better removed at samples with higher pH and final pHs of all samples finally were approximately same (pH=7) due to precipitation of Ca as CaCO3 and consumption of alkalinity. In batch study, investigation of biomass concentration on Ca removal, it was found that Ca removal certainly depends on biological activity. In batch study, investigation of organic matter effect on Ca removal, the most suitable concentration of glucose-COD was 750 mg/L at experimental conditions. The continuous fed study of sludge retention times between about 2 and 20 days on Ca removal showed that SRT is important parameter for Ca removal from Ca-rich wastewaters and optimum SRT was about 5 days in terms of Ca and COD removal at HRT of 11.5 hours. Study showed that HRT is important parameter and HRT of 5-6 hours is optimum for Ca removal from Ca-rich wastewaters. At this HRT, the removal efficiencies of COD, TN, and Ca were obtained a 63 %, 14 % and 72 %, respectively. At obtained optimum SRT and HRT, continuous fed study, investigation of glucose-COD between 0 and 1500 mg/L effect on Ca removal, showed that low levels of COD was also sufficient for calcium removal. The study, carried out to determine urea concentrations between 5-20 mM on ureolytic mixed culture treating synthetic wastewater containing Ca of 15 mM, showed that optimum urea concentration was found as 15 mM for effective Ca removal. In continuous study carried out with a real wastewater of a sugar fabric, BCR reactor established at prior to and recycle of UASB reactor removed efficiently Ca from wastewater. Consequently, the proposed BCR based on MCP can be used in case of reusing of treated Ca-rich wastewater, however the most important disadvantage of this process is N pollution from urea.Key Words: Biocalcification, Carbonate, Industrial Wastewater, Paper, Sugar, Anaerobic, Biotechnology