Optimization of Hydraulic Retention Time (HRT) and Inoculums Addition in Wastewater Treatment Using Anaerobic Digestion System

This research aims to get the optimum combination of Hydraulic Retention Time and addition of inoculums in tofu's wastewater treatment using anaerobic system. Research was done using Central Composite Design (CCD) with two factors, which were Hydraulic Retention Time (12; 18; and 24 hours) and addition of inoculums (5%; 10%; and 15%). The desired responses was percentage decrease of COD, BOD, and TSS; and also increase of pH. According to CCD analysis, the best result was optimally gained on HRT 24 hours and 15% inoculums addition. Those combined factors could decrease COD up to 86. 76%, whereas the decreasing amount of BOD was up to 79.23%, and TSS was up to 67.88%. In addition to those combination, pH of tofu's wastewater increased up to 4.5. That showed that anaerobic system could reduce COD, BOD, and TSS but it couldn’t significantly neutralize pH of tofu's wastewater yet. Due to a 24-hours-anaerobic treatment, the degradation process was still in hydrolytic phase. HRT increase and additions of inoculums, as well as the usage of double treatment system (anaerobic-aerobic; aerobic-anaerobic; anaerobic-anaerobic; or aerobic-aerobic) are required to obtain optimal result.