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RESUMO Sistemas anaeróbios modernos de tratamento de esgoto doméstico, embora bastante eficientes na remoção de matéria orgânica e sólidos em suspensão, não produzem um efluente com qualidade compatível com os padrões legais para descarga em corpos d’água. Por essa razão, esses sistemas têm de ser associados a unidades de pós-tratamento. Este trabalho trata de uma investigação experimental sobre a viabilidade de aplicação do sistema de lodo ativado como uma alternativa do pós-tratamento, especificamente para o caso em que se prevê o efluente final para fertirrigação. Na investigação experimental, utilizou-se um reator de bateladas sequenciais (RBS), em escala laboratorial, como unidade de pós-tratamento. Os resultados experimentais mostraram que o comportamento do sistema RBS pode ser descrito como o modelo geral de lodo ativado da Associação Internacional da Água (IWA, na sigla em inglês), que resulta na definição dos aspectos fundamentais: qualidade do efluente final, consumo de oxigênio e produção de lodo. Na otimização do reator RBS, desenvolveu-se um modelo que permite estabelecer o tempo de permanência mínimo para o pós-tratamento em função de dois parâmetros básicos: a constante de utilização de material orgânico biodegradável pelas bactérias heterotróficas do lodo gerado no sistema de pós tratamento e a sedimentabilidade desse lodo. A constante de utilização de material orgânico foi determinada por testes respirométricos. O lodo gerado no sistema de pós-tratamento surpreendentemente mostrou ter uma sedimentabilidade bem superior àquela normalmente encontrada em sistemas de lodo ativado tratando esgoto bruto, o que constitui um argumento sólido para a aplicação do sistema RBS na prática de pós-tratamento do efluente do reator upflow anaerobic slugde blanket (UASB). ABSTRACT Modern anaerobic systems for domestic sewage treatment, although very effective in removing organic matter and suspended solids, do not produce a quality effluent that complies with the legal standards for discharge into water bodies. Therefore, such systems have to be associated with post treatment units. This paper deals with an experimental investigation into the feasibility of applying the activated sludge system as an alternative post-treatment, specifically for the case where reuse of the final wastewater for fertigation is expected. In the experimental investigation, a pilot-scale sequencing batch reactor (SBR), in laboratory scale, was used as a post-treatment unit. The experimental results showed that the behavior of the RBS system can be described with the general IWA model for activated sludge, resulting in the definition of the fundamental aspects: quality of the final effluent, oxygen consumption, and sludge production. In the optimization of the RBS reactor, a model was developed to establish the minimum retention time for the post-treatment in terms of two basic parameters: the biodegradable organic material utilization constant by heterotrophic bacteria sludge of the post-treatment system and the sedimentability of this sludge. The organic material utilization constant was determined by respirometry testing. The sludge generated in the post-treatment system surprisingly been shown to have a much higher sedimentability than that normally found in activated sludge systems dealing with raw sewage, which is a sound argument for applying the RBS system in the practice of post-treatment reactor effluent UASB

Nos sistemas aeróbios de tratamento de águas residuárias, o oxigênio é um elemento fundamental para que a massa bacteriana possa metabolizar o material orgânico e oxidar compostos como a amônia. Para o acompanhamento desse processo pode ser utilizada a respirometria. Nesta pesquisa, os objetivos são: (1) avaliar a influência da interrupção da aeração sob a atividade das bactérias de sistemas do tipo Bardenpho; (2) estudar a influência do pH na capacidade oxidativa das bactérias nitrificantes; (3) conhecer a faixa de pH ideal para o desenvolvimento das bactérias nitrificantes; e (4) observar a confiabilidade da respirometria no monitoramento da atividade bacteriana. Pôde-se concluir que (1) a capacidade metabólica sofre uma redução gradual na medida em que se aplica um período mais longo sem aeração, (2) o pH influenciou diretamente a atividade das nitrificantes, de forma distinta para a oxidação a nitrito e na oxidação a nitrato, e (3) a respirometria foi uma ferramenta muito útil para avaliar a atividade bacteriana e os sistemas de lodo ativado.

Like all biological wastewater treatment systems, the UASB reactor produces sludge that accumulates in the reactor. Since the storage capacity is limited, the sludge will eventually be discharged together with the effluent, when the reactor is full of sludge. To avoid the discharge of sludge in the effluent, it is necessary that excess sludge be discharged periodically from the reactor before its storage capacity is exhausted. For minimum operational costs it is preferable to have large discharges with a low frequency. On the other hand the discharges cannot be excessive in order to avoid deterioration of the reactor performance after the discharges. An experimental investigation was carried out at pilot scale to establish the influence of the magnitude of excess sludge discharge on the performance of UASB reactors, treating municipal sewage. UASB reactors were operated at hydraulic retention times (HRT) of 4 and 8 h, and excess sludge discharges of varying magnitude were applied. The performance and operational stability of these reactors after the discharges were observed and the sludge accumulation and unintentional discharge (wash-out) with the effluent were determined. During periods of steady state without excess sludge discharge, the sludge production was determined from the settleable solids in the effluent. The data show that for discharges of up to 50% of the sludge mass in reactors with HRT = 4 hours and 60% with HRT = 8 hours, the reactor efficiency and operational stability were affected very little and only during the first few days after the discharge. Discharges of up to 80% of the sludge did not cause instability, but a reduction of the COD removal efficiency was observed during 1 to 2 weeks after the discharge. Independent of the magnitude of sludge discharge, the effluent pH remained in the narrow range of 6.8 to 7.0 and the ratio between alkalinity (average 275 ppm CaCO3) and VFA concentration (average of 28 ppm HAc) was always very high so that there was never a danger of souring of the reactor contents. Based on the obtained experimental data an operational procedure for optimisation of excess sludge discharges was developed. It is believed that along with the favourable natural conditions during the experimental investigation (average temperature of 27°C), the observed reactor stability can be attributed to a large extent to the design of the used phase separator, which is much more efficient than the conventional one. It is possible that results with a conventional UASB reactor would have been different.

A full scale investigation was carried out at the CETREL activated sludge plant to evaluate the technical feasibility of operational cost reduction by planned interruptions of aeration during the daily periods of three hours of high tariff, imposed by the power supply company. It was experimentally established that the daily interruptions did not affect adversely the effluent quality and that sludge activity as well as the settleability remained unaltered. On the other hand the reduction of energy consumption during the high tariff period generated a decrease of operational costs of more than US$ 400.000 per year. Because of the fact that interruptions of aeration in the activated sludge process was shown to be economically feasible, CETREL was in a position of negotiating a more favourable contract with the power supply company, whereby a lower price for power during off peak hours was obtained in exchange for low consumption during the high tariff hours of peak demand.

pH value and stability in anaerobic digesters are governed by the carbonic system. An expression is derived to determine the alkalinity requirement for maintaining a desired pH value in an anaerobic digester. The requirement is calculated from stoichiometric relationships and depends on measurable parameters of the influent (notably concentration of digestible material, influent VFA, alkalinity, acidity and organic nitrogen concentration) and operational conditions (temperature, recycle of effluent and/or biogas). The derived expression is applied to three cases of anaerobic digestion: dilute waste water (sewage), concentrated waste water (vinasse) and sludge. In each case it was calculated if the influent alkalinity was sufficient to maintain an adequate pH for digestion and when it was not, what was the alkalinity requirement to maintain the desired pH value. The calculated values of pH and alkalinity demand compared well with experimental data.

Industrial alcohol production in Brazil is based on fermentation of sugar cane juice. After centrifugation and distillation, azeotropic alcohol is obtained along with four side streams: (1) bagasse, the solid part of the cane plant, (2) yeast, grown during the fermentation, (3) carbon dioxide released during the fermentation and (4) waste water called vinasse composed of the bottom fraction of the distillation and wash waters. The profitability of alcohol distilleries can be improved by a more rational use of the side stream products. The solid products have a diversified application potential. By applying anaerobic digestion to vinasse, methane can be produced at a proportion of 100 kgCH4 per m3 of produced alcohol. Full scale application has shown anaerobic digestion to be technically and economically feasible and the digested waste water can be used for irrigation, whereas the produced solids can be applied as soil conditioners. An alternative for improved energy production is to abandon alcohol fermentation and apply anaerobic digestion directly to the vegetal energy source. In that case the useful energy production is much higher and can be obtained using much simpler equipment. More importantly, the source for energy production would no longer be restricted to cane: Other crops, notably those produced in the drier hinterland of North East Brazil (cassava, sweet potatoes), could also be used for this purpose.

Em condições de casa de vegetação do Centro Nacional de Pesquisa do algodão (Embrapa/CNPA), estudaram-se os efeitos de doses crescentes de lodo de esgoto, caleado a 50% ST - biossólido (equivalentes a 0, 60, 100, 200, 250 e 300 kg N ha-1), sobre a qualidade tecnológica da pluma (finura, resistência, comprimento, uniformidade de comprimento, índice de fibra curta, elongação, fiabilidade, reflectância e grau de amarelo) do algodoeiro herbáceo, variedade BRS 187 8H. O delineamento experimental utilizado foi em blocos ao acaso, com 6 tratamentos e 5 repetições, totalizando 30 unidades experimentais. Cada unidade experimental se constitui de vaso plástico de 90 dm³ que receberam 70 dm³ de solo. Com os resultados obtidos, verificou-se efeito significativo das doses de biossólido sobre as variáveis estudadas. Com o desdobramento da análise de regressão, verificou-se um ajuste quadrático dessas variáveis em função das doses de biossólido. A derivação das equações de regressão estimou que as doses de biossólidos entre 220 e 335 kg N ha-1 proporcionaram o valor máximo para as variáveis de interesse. A dose de biossólido equivalente a 292 kg N ha-1 foi a que proporcionou o valor máximo para a variável resistência de fibra, que é tomada como base de compra do algodão.

O presente trabalho avalia o desempenho de sistemas "wetlands" utilizados no pós-tratamento de efluente de um reator anaeróbio de manta de lodo (UASB), com relação à remoção de matéria orgânica e formas de nitrogênio e fósforo. O reator UASB tratava esgotos sanitários brutos provenientes da cidade de Campina Grande, PB, e o efluente produzido era bombeado para os quatro sistemas "wetlands", em escala piloto, sendo três cultivados com macrófitas emergentes (Juncus sp) e um sem cultivo, para o controle da pesquisa. Todos os sistemas foram operados com diferentes cargas hidráulicas: 4,5; 3,3 e 2,3 cm dia-1. Os resultados obtidos durante as vinte e seis semanas de operação foram promissores e se observaram eficiências médias de remoção de matéria orgânica (DQO) entre 76 e 84%, para cargas aplicadas variando de 6,58 a 14,2 g DQO m-2 dia-1. Na remoção de nutrientes, verificou-se a produção de efluentes com concentrações médias de 6,1 mg N-NH+4 L-1 e com relação ao nitrogênio total: 7,6 NTK mg L-1 com remoção respectivamente de 86 e 87%; já para fósforo total, o sistema "wetlands", operando com carga hidráulica de 2,3 cm dia-1, produziu efluente sem presença de fósforo (100% de remoção). In this paper an evaluation is made of the performance of "wetlands" systems used for post treatment of the effluent from a UASB reactor. The removal of organic material, forms of nitrogen and phosphorus were evaluated. The UASB reactor treats municipal sewage in the City of Campina Grande-Brazil. The produced effluent was pumped to four pilot scale "wetlands" units. Three of these were cultivated with emerging macrophytes (Juncus sp) whereas the fourth was operated without vegetation as a control unit. The three units with vegetation were operated with different hydraulic loads: 4.5, 3.3 and 2.3 cm d-1. The results obtained during the operation period of twenty six weeks were promising. The observed removal efficiencies of organic matter (measured as COD) ranged from 76 to 84% for application load varying from 6.58 to 14.2 g COD m² d-1. With respect to nutrient removal, it is shown that it was possible to produce an effluent with 6.1 mg L-1 N-NH+4 L-1 and 7.6 mg L-1 of TKN with about 86 and 87% removal, respectively, whereas the removal of phosphorus was observed to be 100% in the "wetlands" system operating with a hydraulic load of 2.3 cm d-1.

Traditionally waste stabilisation ponds (WSPs) are built as flow-through systems with an anaerobic, a facultative and one or more maturation ponds in series. The anaerobic pond can be substituted with great advantage by an upflow anaerobic sludge blanket (UASB) reactor. The practical advantages are that the required volume for the UASB reactor is much smaller than the anaerobic pond (20 to 30 times) and that the biogas in the UASB reactor is captured, so that odour problems can be eliminated. The UASB reactor is neighbour friendly and can be used in densely populated areas. The UASB reactor is more efficient than the anaerobic pond, so that the residual organic load is small and the subsequent pond configuration can be designed with the specific purpose of eliminating pathogens. By adopting a plug flow regime, the required area for a particular hygienic effluent quality can be greatly reduced. Also, since the UASB effluent has good transparency, photosynthesis in the ponds is intense and pH increases due to biological carbon dioxide consumption, accelerating the death rate of pathogens and opening the possibility of reducing nutrients: Nitrogen by desorption of gaseous NH3 and phosphorus by phosphate precipitation. The fact that an odour free system with a high quality effluent can be produced in relatively small system composed by a UASB reactor + maturation ponds, increases the applicability of this system for sewage treatment in urban areas. As operation of both UASB and ponds is very simple, several small treatment plants instead of one large central unit may be constructed. Thus a very significant of the sewerage network may be achieved.

Grit removal is a necessary pre treatment step in sewage treatment. Grit can be separated from the liquid phase by gravity settling in a channel. For an adequate performance of the pre treatment unit, it is necessary that the liquid velocity in the channel is kept approximately constant, even when the flow rate varies. This can be accomplished by coupling a channel with a rectangular cross section to a Parshall flume, provided the channel bottom level is placed at a higher level than the flume base. The height of the step between the two devices depends on the magnitude and variation of the sewage flow. At low flow rates the step will start to act as a weir and can take over the function of the Parshall flume as the liquid velocity controlling device, thereby extending significantly the range of flow rates that can be degritted in the pre treatment unit.