A study of start-up process and operation of anaerobic Digestion with coffee pulping waste water

Abstract

One of the major problems that occurs in the application of anaerobic treatment to wastewater is the frequent failure to achieve startup. The start-up period is the time upon which steady state conditions are achieved after which the loading rate can be increased without a deterioration of process efficiency until the maximum load is attained. The main difficulty appears to be the development of the most suitable microbial culture for the wastewater in question. During the study, the start-up process of anaerobic digestion of semi-continuous stirred tank reactors using coffee wastewater was investigated. The start-up procedure involved wastewater analysis, inoculation, stepwise increase of loading rate to a maximum and monitoring the performance of the digesters during the loadi.ng period. The COD of the pulping wastewater was in the range of 9980 to 14200 mg/l and the BOD/COD ratio was about 0.6. Start-up periods based on steady state conditions were found to be in the range of 33 to 44 days fer- biogas sludge and f r e s h cowdunq as inoculum at the two operating temperatures. The loading rates at the start of steady state were in the range of 1.4 to 2.7 kgCOD/m3/d. The maximum laoding rates achievable were 5.7 and 3.0 kgCOD/m3/d at 35°C and ambient temperatures in the range 18°-27°C respectively for biogas sludge. Daily gas production , was recorded to monitor the digesters performance. The gas yields obtained at the start of steady state conditions were in the range of 0.30 to 0.40 m3 / kgCOD removed. The average COD removal s of over 70 percent were achieved at steady state conditions.