Commercial viability of integrated waste treatment in cassava starch industries for targeted resource recoveries

Abstract

The commercial viability of an integrated waste treatment process for converting wastewater and bagasse from a 200 t/d cassava starch facility, together with the associated cassava stalks, into bioenergy products and biofertilizer coupled with recovery of water for reuse, was assessed using Aspen Plus® simulations. The wastewater and bagasse are anaerobically digested for producing biogas that is combusted for thermal energy (Case I), or augmented with CS for combined heat and power production via steam boiler and turbo-generator while recovering biofertilizer in liquid or solid form (Cases II and III). In Case I, the biogas produced meets the thermal energy needs for starch drying in the cassava starch facility. Case II demonstrates energy self-sufficiency for the combined heat and power process and generates 28.53 MW as surplus power that is adequate for meeting power demands from the starch facility (∼2.17 MW) whereas, Case III generates only 56.5% of the biorefinery’s total power demands. In addition, liquid biofertilizer is recovered in Cases I and II while Case III allows for recovery of solid biofertilizer as well as water for reuse in the combined heat and power production, thus reducing the demand for freshwater by 66%. All three cases present potential profitable commercial investment with Net Present Values between US$ 83.4 million and 130 million, depending mainly on wastewater treatment costs and bioelectricity prices, and minimally on biofertilizer and thermal energy prices. Thus, the integration of water recovery and cassava stalks conversion into cassava waste treatment results in both economic and environmental benefits for the cassava starch industries.