Lívia Cristina da Silva Lobato

Estimates of methane loss and energy recovery potential in anaerobic reactors treating domestic wastewater

This work aimed at developing a mathematical model that could estimate more precisely the fraction of chemical oxygen demand (COD) recovered as methane in the biogas and which, effectively, represented the potential for energy recovery in upflow anaerobic sludge blanket (UASB) reactors treating domestic wastewater. The model sought to include all routes of conversion and losses in the reactor, including the portion of COD used for the reduction of sulfates and the loss of methane in the residual gas and dissolved in the effluent. Results from the production of biogas in small- and large-scale UASB reactors were used to validate the model. The results showed that the model allowed a more realistic estimate of biogas production and of its energy potential.

Experience with the design and start up of two full-scale UASB plants in Brazil: enhancements and drawbacks

This paper discusses the main drawbacks and enhancements experienced with the design and start up of two full-scale UASB plants in Brazil. The topics addressed are related to blockage of inlet pipes, scum accumulation, seed sludge for the start-up, corrosion and gas leakage, odour generation and sludge management. The paper describes the main improvements achieved.

Use of biogas for cogeneration of heat and electricity for local application: performance evaluation of an engine power generator and a sludge thermal dryer.

A small unit of cogeneration of energy and heat was tested at the Centre for Research and Training on Sanitation UFMG/COPASA - CePTS, located at the Arrudas Sewage Treatment Plant, in Belo Horizonte, Minas Gerais, Brazil. The unit consisted of an engine power generator adapted to run on biogas, a thermal dryer prototype and other peripherals (compressor, biogas storage tank, air blower, etc.). The heat from engine power generator exhaust gases was directed towards the thermal dryer prototype to dry the sludge and disinfect it. The results showed that the experimental apparatus is self-sufficient in electricity, even producing a surplus, available for other uses. The tests of drying and disinfection of sludge lasted 7 h, leading to an increase in solids content from 4 to 8% (50% reduction in sludge volume). Although the drying of sludge was not possible (only thickening was achieved), the disinfection process proved very effective, enabling the complete inactivation of helminth eggs.

Biological sulphide removal from anaerobically treated domestic sewage: reactor performance and microbial community dynamics

We developed a biological sulphide oxidation system and evaluated two reactors (shaped similar to the settler compartment of an up-flow anaerobic sludge blanket [UASB] reactor) with different support materials for biomass retention: polypropylene rings and polyurethane foam. The start-up reaction was achieved using microorganisms naturally occurring on the open surface of UASB reactors treating domestic wastewater. Sulphide removal efficiencies of 65% and 90% were achieved with hydraulic retention times (HRTs) of 24 and 12 h, respectively, in both reactors. However, a higher amount of elemental sulphur was formed and accumulated in the biomass from reactor 1 (20 mg S0 g−1 VTS) than in that from reactor 2 (2.9 mg S0 g−1 VTS) with an HRT of 24 h. Denaturing gradient gel electrophoresis (DGGE) results revealed that the the pink and green biomass that developed in both reactors comprised a diverse bacterial community and had sequences related to phototrophic green and purple-sulphur bacteria such as Chlorobium sp., Chloronema giganteum, and Chromatiaceae. DGGE band patterns also demonstrated that bacterial community was dynamic over time within the same reactor and that different support materials selected for distinct bacterial communities. Taken together, these results indicated that sulphide concentrations of 1–6 mg L−1 could be efficiently removed from the effluent of a pilot-scale UASB reactor in two sulphide biological oxidation reactors at HRTs of 12 and 24 h, showing the potential for sulphur recovery from anaerobically treated domestic wastewater.

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).