Abstract
Tapioca is a starch extracted from cassava root. Major problems in the tapioca production are the reduction of cassava yield per hectare brought by the decrease in soil fertility and the huge emission of greenhouse gas from the lagoon treating tapioca mill effluent. Integrated biomass residue recycle system consists of beef cattle fattening by using solid biomass residue as a feed and methane fermentation of the mill effluent has a potential for solving those problems. Composted cattle manure can be used to increase the soil fertility of cassava field by increasing the organic content in the soil. Methane fermentation can supply energy for the tapioca mill and thus decrease the emission of green house gas from the lagoon. Information on material flow of biomass residue and wastewater in both recycle process and tapioca mill is needed to design the appropriate biomass residue and wastewater recycle system. Weight-base material flow analysis as well as carbon and nitrogen flow on tapioca mill and on the recycle process of biomass residue and wastewater have been carried out in Sumatra, Indonesia. It was clarified that 204 kg tapioca, which contained 71.6 kg organic carbon, was produced from 1 ton of cassava, which contained 164 kg organic carbon, in the small scale tapioca mill. From the tapioca mill 46.7 kg (28.5％) and 40.4 kg (24.6％) organic carbon contained in the cassava were discharged into the wastewater and the onggok, solid biomass residue, respectively. Carbon and nitrogen flow in the beef cattle fattening shows that the onggok discharged from 5 t cassava processing are needed to bring 200 kg weight gain of beef cattle, whereas additional corn and formula feed are required. The quantity of wastewater was 2.40 m3 per one ton of cassava and 6.93 m3 of methane was produced from the wastewater in the lagoon. The quantity of methane will be enough to supply energy for the electric power generation by engine generator in this small mill. 190 kg tapioca was produced from 1 ton of cassava in the large scale tapioca mill. 40.7％, 21.8％ and 20.5％ of organic carbon contained in the cassava were observed in the tapioca, the onggok and the wastewater, respectively. The quantity of wastewater was 3.25 m3 per one ton of cassava with average COD＝20,278 mg/L. Wastewater of tapioca mill was mixed with that of pineapple processing and treated by using UASB type methane fermentation reactor. Methane yield was as high as 280 L/kg-COD under the volumetric loading of 6.5 kg-COD/m3d of the reactor.
