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In Brazil cane is being been grown at large scale to produce alcohol as an automotive fuel. Alcohol is the sole product, but there is generation of a large quantity of gaseous (CO2), liquid (vinasse) and solid (bagasse) by-products, which currently have very little or even negative value. By using steam turbines fuelled with bagasse combustion, electric power can be generated at a rate of 1 MWh per m3 of produced alcohol. Anaerobic digestion can be applied to vinasse to produce enough biogas for 0.5 MWh per m3 of alcohol, bringing total electric power production from subproducts to 1.5 MWh per m3 of alcohol. These operations are presently implemented at some distilleries at full scale. It has been shown at bench scale that by applying anaerobic digestion also to bagasse and burning the non-biodegradable residual, the power output can be increased to 2.25 MWh per m3 of alcohol, but the economic feasibility of this option depends on the maximum loading rate of the bagasse digester and the energy price. At the current alcohol production level of 13 × 106 m3/year, the power generation potential is 2.2 GW, which represents 4% of the power demand in Brazil. The digested waste water contains about 70% of the nutrient demand of the cane fields, which can be recycled. A preliminary economic evaluation shows that productive use of the subproducts of alcohol distilleries is economically feasible if the price is more than US$30 per MWHh, which is the current sales price in Brazil. Another important advantage of the rational use of by-products is that the generation of electric power has the potential to reduce the emission of CO2 to the atmosphere by 0.8–1.2 t per m3 of alcohol compared to generation using natural gas.

This papers describes the behaviour of wetlands as a post-treatment unit for anaerobically treated sewage for the removal of organic matter, suspended solids, nutrients (nitrogen and phosphorus) and faecal coliforms. Raw sewage was treated in a UASB reactor with a retention time of 5 h and the effluent was used in four units of wetlands with coarse sand as the medium and operated with different hydraulic loads. Three of the units had emerging macrophytes (Juncus sp), whereas the fourth one was operated as a control unit without plants. During the 12 months of operation, the organic material removal efficiency (measured as COD) was in the range of 79 to 85%, whereas suspended solids removal varied from 48 to 71%. Faecal coliform removal was very high (99,99%); phosphorus was also efficiently removed (average efficiency of 90% for the lowest hydraulic load), but nitrogen removal was only partial (45 to 70% for ammonia and 47 to 70% for TKN). The experimental results clearly show the technical feasibility of using wetlands for treatment of municipal sewage after a pre-treatment in the UASB reactor.

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