André Pereira Rosa

Energy potential and alternative usages of biogas and sludge from UASB reactors: case study of the Laboreaux wastewater treatment plant

This work assessed the energy potential and alternative usages of biogas and sludge generated in upflow anaerobic sludge blanket reactors at the Laboreaux sewage treatment plant (STP), Brazil. Two scenarios were considered: (i) priority use of biogas for the thermal drying of dehydrated sludge and the use of the excess biogas for electricity generation in an ICE (internal combustion engine); and (ii) priority use of biogas for electricity generation and the use of the heat of the engine exhaust gases for the thermal drying of the sludge. Scenario 1 showed that the electricity generated is able to supply 22.2% of the STP power demand, but the thermal drying process enables a greater reduction or even elimination of the final volume of sludge to be disposed. In Scenario 2, the electricity generated is able to supply 57.6% of the STP power demand; however, the heat in the exhaust gases is not enough to dry the total amount of dehydrated sludge.

NOTA TÉCNICA: APROVEITAMENTO ENERGÉTICO DOS SUBPRODUTOS, LODO E BIOGÁS, A PARTIR DO TRATAMENTO ANAERÓBIO DE EFLUENTES PELO USO DE PROCESSOS TERMOQUÍMICOS

O processo anaerobio tem sido amplamente utilizado no Brasil para o tratamento de efluentes sanitarios e industriais em virtude de suas vantagens ja reconhecidas. Em contrapartida, seus principais subprodutos gerados, lodo e biogas, tem tido como principais alternativas de destino final o aterro sanitario e a queima direta, respectivamente, o que resulta em elevados gastos com transporte e desperdicio de seu potencial energetico. Considerando os beneficios referentes a recuperacao energetica do lodo, os processos termoquimicos tem ganhado destaque, sendo que os mais relevantes sao a pirolise, a gaseificacao e a combustao. No que se refere ao biogas, a recuperacao deste subproduto para fins energeticos pode contribuir com a geracao de energia termica e/ou eletrica, em adicao, o uso conjunto dos subprodutos podem conferir beneficios as plantas de tratamento sob a perspectiva ambiental, tecnica e economica ao favorecer o gerenciamento dos mesmos e reduzir a demanda por outras fontes de energia. Esta nota tecnica tem o objetivo de apresentar algumas das configuracoes fazendo uso das principais tecnologias de processos termoquimicos aplicadas ao lodo, e seu uso consorciado com a recuperacao do biogas em beneficio das unidades que promovem o tratamento de efluentes pela via anaerobia.

Energy potential and alternative usages of biogas and sludge from UASB reactors: case study of the Laboreaux wastewater treatment plant (Itabira) / Potencial energético e alternativas para o aproveitamento do biogás e lodo de reatores UASB: Estudo de caso Estação de tratamento de efluentes Laboreaux (Itabira)

This work assesses the potential of energy recovery of the byproducts biogas and sludge produced at the Laboreaux wastewater treatment plant (WWTP), in Itabira (MG), which is integrated by UASB reactors, trickling filters and sludge dehydration unit (filter press). The byproducts biogas and sludge were quantitatively (production) and qualitatively (composition and calorific value) characterized during a monitoring period of 12 months. Two scenarios for energy recovery from the byproducts were considered: (i) priority use of biogas for sludge thermal drying and the excess of biogas being used for power generation in an internal combustion engine (ICE); and (ii) primary use of biogas for power generation and the heat of the engine exhaustion gases being used for sludge thermal drying. Biogas burning conditions into a combustion chamber and in an internal combustion engine, as well as mass and energy balances for each scenario, were assessed with the CHEMCAD(r) software. The study analysed the potential use of the byproducts as sources of renewable energy for use in the WWTP itself and to be offered to third party. In scenario 1, the electricity generation is lower (fulfilling 22.2% of the WWTP energy demand), but thermal drying allows greater reduction of sludge volume to be disposed of, or the entire elimination of final disposal if the dry sludge (with 10% moisture content) is used as fuel by the third party. As for scenario 2, the electricity generation is sufficient to supply 57.6% of the WWTP energy demand, nevertheless the heat contained in exhausted gases is not enough to dry the whole dehydrated sludge, configuring a lower reduction of sludge amount to be disposed of (13.5 or 24.9% of mass reduction, depending on the moisture reduction alternative chosen).