The dissolved methane recovery from treated sewage in upflow anaerobic sludge blanket (UASB) reactors: The energy demand, carbon footprint and financial cost.

The goal of this research was to quantify the energy demand and carbon footprint over the life cycle, along with the financial cost, of sewage treatment with the recovery of dissolved methane (d-CH4). The sewage treatment is composed of pre-treatment, followed by treatment in upflow anaerobic sludge blanket (UASB) reactors, trickling filter and secondary decanter, post-treatment with disinfection, and biogas recovery in the three-phase separator of the UASB reactor. The methods used in this study were attributional life cycle assessment and techno-economic analysis - LCA and TEA, respectively. The energy demand, carbon footprint and financial cost for 1 m3 sewage treatment in the evaluated scenario without d-CH4 recovery (S1) were 3.4 MJ, 1.7 kg CO2eq and 0.17 USD respectively, while those with d-CH4 recovery (S2) varied by 12%, -16% and 2.3% compared to S1. The produced biogas for lower heating value in S2 (2.6 MJ) was 27% higher than that in S1 (2.0 MJ) and this varied from 1.3 MJ to 4.6 MJ in the scenarios for different influent chemical oxygen demand (COD) in the sewage treatment plant (STP) and COD removal efficiency in the UASB reactor. The highest eco-efficiency for 1 MJ heat production from the STP biogas was achieved in the scenario with d-CH4 recovery, higher influent COD, higher COD removal efficiency in the UASB reactor, d-CH4 saturation, photovoltaic electricity supply, and a higher energy efficiency in d-CH4 recovery combined (S2,COD+,R+,S,PV,EE+), which reduced the energy demand by 55%, carbon footprint by 66% and financial cost by 63% compared to S1. Furthermore, the STP functionality change from a single-product (biogas) to a multi-product (biogas, water for reuse and biosolid fertilizer) approach (S1,WR, BF and S2,WR,BF) made the biogas a competitive product compared to those from fossil sources. Therefore, resource recovery from the sewage treatment in higher influent COD, higher COD removal efficiency, the use of a more efficient, clean and economical electricity source and higher energy efficiency in d-CH4 recovery in a multi-product STP contribute to achieving the energy self-sufficiency over the life cycle while reducing the carbon footprint and financial cost of its products.

Potential benefits of near critical and supercritical pre-treatment of lignocellulosic biomass towards anaerobic digestion.

Vegetable crop residues, such as sugarcane bagasse (SCB), despite their limited biodegradability, are potential materials for anaerobic processes because of their low cost, high availability, and sugar content. The difficulty of biodegrading this type of material is primarily related to its chemical composition and to the complex interactions between its compounds (cellulose, hemicelluloses, and lignin). Thus, the following supercritical and near critical carbon dioxide (CO2) pre-treatments were evaluated with and without the addition of sodium hydroxide (NaOH): (i) 40°C/70 kgf·cm-2; (ii) 60°C/200 kgf·cm-2; and (iii) 80°C/200 kgf·cm-2, aiming to enhance the anaerobic biodegradability of SCB. The methanogenic production of SCB increased in all cases in which the material was pre-treated, except the case in which NaOH was used together with a high temperature. The condition using CO2 at 60°C/200 kgf·cm-2 was highlighted with a lignin removal of 8.07% and an accumulated methane production of 0.6498 ± 0.014 LN (273.15K, 1.01325 × 105 Pa), 23.4% higher than the value obtained with the untreated material. This condition also showed the highest net energy at the energy balance that was calculated for comparison with the tested conditions. The results showed that pre-treatments with near critical and supercritical fluids have the potential to reduce structural obstacles of lignocellulosic materials and to enhance their anaerobic biodegradability.

BTEX removal in a horizontal-flow anaerobic immobilized biomass reactor under denitrifying conditions.

Because benzene, toluene, ethylbenzene, and xylenes (BTEX) and ethanol are important contaminants present in Brazilian gasoline, it is essential to develop technology that can be used in the bioremediation of gasoline-contaminated aquifers. This paper evaluates the performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor fed with water containing gasoline constituents under denitrifying conditions. Two HAIB reactors filled with polyurethane foam matrices (5 mm cubes, 23 kg/m(3) density and 95 % porosity) for biomass attachment were assayed. The reactor fed with synthetic substrate containing protein, carbohydrates, sodium bicarbonate and BTEX solution in ethanol, at an Hydraulic retention time (HRT) of 13.5 h, presented hydrocarbon removal efficiencies of 99 % at the following initial concentrations: benzene 6.7 mg/L, toluene 4.9 mg/L, m-xylene and p-xylene 7.2 mg/L, ethylbenzene 3.7 mg/L, and nitrate 60 mg N/L. The HAIB reactor fed with gasoline-contaminated water at an HRT of 20 h showed hydrocarbon removal efficiencies of 96 % at the following initial concentrations: benzene, 4.9 mg/L; toluene, 7.2 mg/L; m-xylene, 3.7 mg/L; and nitrate 400 mg N/L. Microbiological observations along the length of the HAIB reactor fed with gasoline-contaminated water confirmed that in the first segment of the reactor, denitrifying metabolism predominated, whereas from the first sampling port on, the metabolism observed was predominantly methanogenic.

Evaluating the potential of a new reactor configuration to enhance simultaneous organic matter and nitrogen removal in dairy wastewater treatment.

The dairy industry is a very productive sector worldwide and known for producing great volumes of wastewater that is rich in organic matter and nutrients. Apart from fat, the organic matter in such effluents is easily degradable, demanding an external carbon source for conventional denitrification. In this manner, new configurations of reactors promoting a suitable environment for more sustainable nitrogen removal are beyond required-they are paramount. Therefore, the performance of a structured-bed hybrid baffled reactor (SBHBR) with anaerobic and oxic/anoxic chambers was designed and assessed for treating different dairy wastewaters. A combination of baffled and biofilm-structured systems under intermittent aeration was the solution proposed to obtain a new method for nitrogen removal under low COD/TN ratios. The COD/TN ratios tested were 2.1 ± 0.6, 0.84 ± 0.5, and 0.35 ± 0.1 in the inlet of the O/A chambers for operational stages I, II, and III, respectively. The SBHBR provided COD removal efficiencies above 90% in all experimental stages. During stage III, the process had nitrification and denitrification efficiencies of 85.9 ± 17% and 85.2 ± 9%, respectively, resulting in a TN removal efficiency of 74.6 ± 14.7%. Stoichiometric calculations were used to corroborate the activity of bacteria that could perform the anammox pathways as their main mechanisms.

Effect of impeller type and agitation on the performance of pilot scale ASBR and AnSBBR applied to sanitary wastewater treatment.

The objective of this work was to assess the effect of agitation rate and impeller type in two mechanically stirred sequencing batch reactors: one containing granulated biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam (denominated AnSBBR). Each configuration, with total volume of 1 m(3), treated 0.65 m(3) sanitary wastewater at ambient temperature in 8-h cycles. Three impeller types were assessed for each reactor configuration: flat-blade turbine impeller, 45 degrees -inclined-blade turbine impeller and helix impeller, as well as two agitation rates: 40 and 80 rpm, resulting in a combination of six experimental conditions. In addition, the ASBR was also operated at 20 rpm with a flat-blade turbine impeller and the AnSBBR was operated with a draft tube and helix impeller at 80 and 120 rpm. To quantify how impeller type and agitation rate relate to substrate consumption rate, results obtained during monitoring at the end of the cycle, as well as the time profiles during a cycle were analyzed. Increasing agitation rate from 40 rpm to 80 rpm in the AnSBBR improved substrate consumption rate whereas in the ASBR this increase destabilized the system, likely due to granule rupture caused by the higher agitation. The AnSBBR showed highest solids and substrate removal, highest kinetic constant and highest alkalinity production when using a helix impeller, 80 rpm, and no draft tube. The best condition for the ASBR was achieved with a flat-blade turbine impeller at 20 rpm. The presence of the draft tube in the AnSBBR did not show significant improvement in reactor efficiency. Furthermore, power consumption studies in these pilot scale reactors showed that power transfer required to improve mass transfer might be technically and economically feasible.

Anaerobic digestion of aqueous phase from hydrothermal liquefaction of Spirulina using biostimulated sludge.

Hydrothermal liquefaction is a process that converts wet biomass into biofuels, more specifically bio-crude oil. During the process, post hydrothermal liquefaction waste water (PHWW) is generated, rich in nutrient and organic matter, however potentially toxic. Anaerobic digestion of PHWW from Spirulina, was evaluated using biostimulated sludge as a strategy to optimize the process. The biostimulation was conducted in a sequential batch reactor fed with organic acids and methanol aiming at development of acetogenic and methanogenic microorganism. Anaerobic biodegradability batch assays were performed, with biostimulated sludge and with non-biostimulated sludge, using increasing PHWW concentrations. Biostimulated sludge were more favourable for reaching higher methane yields at higher organic matter concentrations in comparison to non-biostimulated sludge, presenting less inhibition at conditions tested. Biostimulation was a key process to select and favour potential microorganisms involved in specialized uptake of recalcitrant compounds, such as Mesotoga and Methanomethylovorans.

Effect of feeding strategy on a stirred anaerobic sequencing fed-batch reactor containing immobilized biomass.

The present work reports on the influence of feeding strategy on the stability and performance of a stirred anaerobic sequencing fed-batch reactor containing biomass immobilized on polyurethane foam. The reactor treated low-strength wastewater and was operated at 30 degrees C with an agitation rate of 200 rpm. A 180-min cycle was used to treat approximately 0.5 l of synthetic substrate with a chemical oxygen demand concentration of nearly 500 mg/l. The reactor was operated in batch mode with a 3-min feeding step and in constant rate fed-batch mode with feeding steps of 30, 60 and 180 min. During batch operation, the system attained stability and had a removal efficiency of 86% based on non-filtered substrate concentration. However, during fed-batch operation stability and efficiency were impaired and formation of suspended material was identified. Stability was achieved only for the 30-min feeding step. The poor performance and instability observed in the fed-batch experiments were credited to the formation of considerable quantities of extracellular polymers, which impeded contact between substrate and biomass with consequent negative effect on the mass transfer fluxes. The biopolymer formation was very likely a result of the fed-batch operational mode, in which part of the bioparticles were deprived of contact with the liquid medium for a relatively long period of time.

Caracterização e cinética do tratamento anaeróbio de efluentes de laticínios / Characterization and kinetics of the anaerobic treatment of dairy wastewaters

A geração de efluentes do setor de laticínios é imensa e, em função do conteúdo emulsionado de gorduras, tais efluentes são tidos como de difícil degradação. O presente artigo teve como objetivo a caracterização dos efluentes gerados por um laticínio que processa 800 L de leite por dia, relacionando suas características com as ocorrências na planta. Este laticínio produz leite pasteurizado, mussarela, queijo Minas frescal, sorvete e iogurte. O efluente dos processos concomitantes de produção de mussarela e pasteurização de leite foi utilizado para alimentação de um reator UASB (upflow anaerobic sludge blanket) híbrido (UASBh), e através da aplicação de cargas orgânicas volumétricas crescentes, foi realizado o estudo cinético do sistema. A maior carga específica calculada para os efluentes estudados foi referente ao processamento de mussarela, em função do abundante volume de soro descartado. As concentrações de sais e metais encontradas nos efluentes analisados se mostraram muito aquém das recomendadas como necessárias ao balanceado crescimento do consórcio anaeróbio. A concentração de lipídeos não representou problema em efluentes da produção de iogurte, uma vez que foram sempre inferiores a 18,9 mg.L-1 (valores típicos de efluentes diluídos). O reator do tipo UASBh operou de forma estável com carga orgânica volumétrica (COV) média aplicada de até 8,9 kg.m-3.d-1, carga esta superior à preconizada na literatura como segura. Com COV média aplicada de 15,4 kg.m-3.d-1, a velocidade de consumo de substrato não acompanhou o aumento da oferta, mantendo-se praticamente constante, resultando em queda na eficiência do processo e em sua estabilidade.

The generation of effluents from the dairy industry is huge and deemed difficult degradation, depending on the content of emulsified fats.This study aimed to characterize the effluent emitted by a dairy which process 800 L of milk daily, relating its features to the events at the plant. The plant processes pasteurized milk, cheese, ice-cream and yogurt. The effluent of the concurrent processes of mozzarella making and milk pasteurization was used to power a hybrid UASB reactor. By applying increasing volumetric organic loads, we performed a kinetic study of the system. The most specific charge calculated for the effluent was from the mozzarella processing due to the large volumes of whey discarded. The concentrations of salts and metals found in wastewater analyzed were very below to the required and recommended by balanced growth of the anaerobic consortium. The lipids concentration in effluent was not a problem in the production of yogurt, since they were lower than 18.9 mg L-1 (typical values of diluted effluents). The UASBh reactor presented stability when the applied organic loading rate (OLR) was until 8.9 kg.m-3.d-1. With superior values, the rate of substrate consumption did not follow the increase in supply of organic matter, remaining almost constant, resulting in a drop in efficiency and stability.

Remoção de etanol e benzeno em reator anaeróbio horizontal de leito fixo na presença de sulfato / Ethanol and benzene removal in a horizontal-flow anaerobic immobilized biomass reactor in the presence of sulfate

Reator anaeróbio horizontal de leito fixo (RAHLF), preenchido com espumas de poliuretano, foi usado para tratar benzeno em solução etanólica, sob condições sulfetogênicas. Benzeno foi adicionado em concentração inicial de 2,0 mg.l-1, seguido de aumentos que variaram até 10 mg.l-1. O etanol foi adicionado em concentrações de 170 mg.l-1 a 980 mg.l-1. Soluções de sulfato ferroso e sulfato de sódio foram usadas, nas concentrações de 91 e 550 mg.l-1, respectivamente. O reator foi operado a 30 (± 2) ºC com tempo de detenção hidráulica de 12 h. A remoção da matéria orgânica foi próxima a 90 por cento com taxa máxima de degradação de benzeno de 0,07 mg benzeno.mg-1SSV.d-1. O presente trabalho corrobora os dados obtidos por Cattony et al (2005), na medida em que torna mais consistente a proposta do uso de unidades compactas de RAHLF, para a biorremediação in situ de compostos aromáticos.

In this study it is reported the operation of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor under sulfate-reducing condition which was also exposed to different amounts of ethanol and benzene. The HAIB reactor comprised of an immobilized biomass on polyurethane foam and ferrous and sodium sulfate solutions were used (91 and 550 mg.l-1, respectively), to promote a sulfate-reducing environment. Benzene was added at an initial concentration of 2.0 mg.l-1 followed by an increased to 9 e 10 mg.l-1, respectively. Ethanol was added at an initial concentration of 170 mg.l-1 followed by an increased range of 960 mg.l-1. The reactor was operated at 30 (± 2) ºC with hydraulic detention time of 12 h. Organic matter removal efficiency of 90 percent with a maximum benzene degradation rate of 0.07 mg benzene.mg-1VSS.d-1. Thus, this work corroborate the data obtained for Cattony et al (2005) and also demonstrate that compact units of HAIB reactors, under sulfate reducing conditions, are a potential alternative for in situ aromatic compounds bioremediation.

Morphological study of biomass during the start-up period of a fixed-bed anaerobic reactor treating domestic sewage

Este trabalho apresenta um estudo morfológico de microrganismos aderidos à espuma de poliuretano em reator anaeróbio horizontal de leito fixo (RAHLF), aplicado ao tratamento de esgoto sanitário. O processo de colonização do suporte pela biomassa anaeróbia e as características morfológicas das células aderidas foram monitorados durante o período de partida do reator. Bacilos e cocos não fluorescentes foram predominantes no processo de aderência direta à espuma de poliuretano. Aumento na diversidade biológica foi observado a partir da 10ª semana de operação do reator, com predominância de bacilos, cocos e arqueas metanogênicas semelhantes a Methanosaeta. Problemas hidrodinâmicos, tais como formação de canais preferenciais e colmatação do leito, foram observados no reator, principalmente devido ao acúmulo de polímeros extracelulares nos interstícios do leito. Este material acumulou principalmente nos estágios iniciais do reator, causando a diminuição gradativa do desempenho do processo anaeróbio de conversão da matéria orgânica. Os resultados demonstraram a importância e utilidade do monitoramento da dinâmica de formação do biofilme durante o período de partida de reatores, com resultados positivos para identificação de problemas operacionais.