Deconcentration of Chromium Contained in Wastewater Using a Bacteria and Microalgae Consortia with a High Rate Algal Reactor System

Heavy metal pollution has recently gained serious attention as an environmental issue. One example of heavy metal pollution in the natural water environment is chromium metal, which is released by several industries. Polyvalent chromium 6 is one of the most difficult environmental pollutants to remove due to its dissolvable and unstable properties. Bioremediation using a consortium of bacteria and microalgae in a High Rate Algal Reactor (HRAR) system can be expected to decrease the chromium concentration. The aim of this study was to determine the percentage of chromium removal by a bacteria and microalgae consortium and to determine the best ratio between these two kinds of microorganism in the context of pollutant reduction. The wastewater containing chromium that was used in this study was artificial wastewater with a chromium concentration of 17 mg/L. The species of microalgae and bacteria were Chlorella vulgaris and Azotobacter S8. The chromium concentration used in the main experiment was determined through a preliminary Range Finding Test (RFT) for the microalgae and Minimum Inhibitory Concentration (MIC) for the bacteria. The chromium concentrations in RFT and MIC were 0, 17, 42, 85, 169 and 339 mg/L and the variables in the main study were the respective Azotobacter S8 and Chlorella vulgaris compositions (50:50, 75:25, 25:75 %v/v). This, in addition to the variation in the consortium composition, was compared to the polluted media in the reactor (5:95 and 10:90 %v/v). Such parameters as pH, temperature, total chromium concentration, microalgae cell count, and bacterial colonies were monitored during the experiments. The chromium deconcentration study was conducted over 7 (seven) days in a High Rate Algal Reactor (HRAR) with the microorganism inoculation conducted in the determined composition of artificial wastewater. The reactor was stirred for 24 hours per day and illuminated using artificial light at an intensity of 6000 – 7000 lux. The deconcentration of chromium was analyzed using an Atomic Adsrober Spectrophotometer (AAS). The results showed that the highest chromium removal was reached in the reactor where the ratio of microorganisms and bacteria was 50%:50%, the initial inoculum of polluted media was 5%: 95% and there was a chromium removal rate of 18.68%. The consortium of Azotobacter S8 bacteria and Chlorella vulgaris microalgae can thus reduce the chromium concentration through the mechanisms of biosorption, bioaugmentation, and bioaccumulation.