Calcium removal from calcium rich paper mill wastewater by microbial CaCO3 precipitation

Abstract

High concentrations of calcium present in paper mill wastewaters are considered as they lead to some important problems during the treatment process. Recently, submerged membrane bioreactor (sMBR) system have been commonly used to industrial wastewater treatment and it is observed that membrane scaling or fouling is one of the most important problems which causes many operational difficulties. A decrease in membrane flux is observed after the formation of CaCO3 film on the membrane surface as inorganic membrane fouling is encountered during the operation of the sMBR. Microbial carbonate precipitation (MCP) process is a natural microbial process and the mechanism of MCP is defined as the ability of microorganism to alkalinise an environment through various physiological activities. The purpose of this study was to investigate the application of MCP to paper-mill wastewater as a pre-treatment method prior to submerged membrane bioreactor. The potential for CaCO3 removal from wastewater through urea was investigated at optimum operation conditions obtained from the batch tests using a sequencing batch reactor (SBR). The optimum dosage of urea and HRT were determined 4 g/L and 72 h. The results obtained indicated that the calcium removal efficiency was found to be 90.16% at optimum experimental conditions in the SBR operation. It was found out that the MCP was a suitable method for calcium removal and it can be used as a pre-treatment method of paper-mill wastewater treatment to avoid calcium scaling and inorganic fouling in sMBR in the study.