Hexavalent chromium is one of the toxic metals in water pollution. This study is aimed at analyzing the involvement of chromium reductase and biosorption potential in chromium-resistant species of Bacillus cereus. A total of 10 % (v/v) of B. cereus biomass was inoculated into a 90 mL chromium-contaminated solution with an initial concentration of 60 mg/L. Biomass digestion was carried out every day for a 5-day treatment period for chromium content analysis, while biomass characterization was carried out at the end of the treatment period, comparing the exposed vs. non-exposed bacteria. Results indicated that the highest chromium removal (16.12 ± 0.63 %) was obtained on day 3, while the maximum biosorption capacity was obtained on day 1, reaching 0.461 ± 0.02 mg Cr/g dry cell of biomass. XRD showed the crystalline structure of the bacteria cell after being exposed to chromium, suggesting that interactions between polysaccharides and proteins in the membrane may occur during the treatment. In addition, FT-IR spectra also showed decreasing peaks and the involvement of hydroxyl, carboxyl, carbonyl, and nitroxide groups during the treatment. SEM-EDX results indicated that bacteria are experiencing cell structure alteration with more intense chromium spectra on the surface, while TEM images showed endospore formation by B. cereus under adverse environmental conditions. This study suggested that the removal of hexavalent chromium by B. cereus might be dominant via biosorption (translocated into cell biomass).

Tofu effluent contains a high concentration of organic materials, nutrients, suspended solids and is also low in pH. This research was aimed at applying phytotreatment using floating plant species of Pistia stratiotes to polish tofu effluent before final discharge into water bodies while also producing biogas from the resultant biomass after treatment. A range-finding test (RFT) was conducted to determine the initial concentration to be treated and resulted in 10 % tofu effluent. Phytotreatment was conducted for a period of 14 days, focusing on the removal of organic matter and nutrient contents. After 14 days of treatment, P. stratiotes were able to remove total suspended solids (TSS) by 88 %, ammonia by 42.3 %, phosphate by 50 %, chemical oxygen demand (COD) by 84 %, and biological oxygen demand (BOD) by 95 %, significantly higher as compared to control. Phytotreatment was able to stabilize pH to a neutral value, and P. stratiotes were able to transfer oxygen from air to the rhizosphere area. The maximum daily production of biogas using the plant's biomass was higher as compared to the control; however, the overall biogas accumulation was significantly lower during the 45 days of observation. Further biomass pretreatment was suggested before digestion to obtain higher biogas production since the cellulose, hemicellulose, and lignin content inside the plant biomass were subjected to being hardly degraded by the anaerobic microorganisms.