Formation of soluble microbial products (SMP) in anaerobic reactors during stress conditions

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Anaerobic wastewater treatment has many advantages over aerobic treatment, however, one factor that limits its application is the relatively high concentration of organic material in the effluent. Characterization of both aerobic and anaerobic effluents has shown that the majority of the residual chemical oxygen demand (COD) is due to soluble microbial products (SMP) produced by biomass during the treatment. Although the importance of SMP has already been acknowledged in the literature, there is very little information about their composition, the mechanisms that lead to their formation, and the environmental factors and operational parameters that affect their production, particularly for anaerobic systems operated under transient stress conditions. Therefore, the main objectives of this thesis were to investigate the effects of transient hydraulic and shock loads, as well as of the stressful conditions of nutrient deficiency and the presence of toxic compounds on SMP production. The SMP produced by anaerobic reactors was classified by molecular weight distribution and chemical analyses, and identified by mass spectrometry techniques. The results showed that SMP production increased during both organic and hydraulic shock loads, and that cell lysis seemed to be an important source of SMP during hydraulic shock loads and low pHs. The production of SMP also increased in the absence of nutrients and in the presence of the toxic compounds chromium and chloroform. Chemical characterization showed that protein and carbohydrate could account for no more than 50% of the residual COD under such conditions, and that some specific SMPs might have been released as a strategic response to the stress. Experiments using biochemical methane assays (BMP) associated with metal distribution showed that specific microbial compounds seemed to be deliberately released in solution to aid in the uptake of some metal nutrients, and to alleviate metal toxicity via efflux pumps. Characterization of anaerobic effluents by gas chromatography-mass spectrometry (GC-MS) showed the presence of many aromatic compounds, and chromatographic analyses revealed that cell lysis and extracellular polymers (ECP) were important sources of SMP. Finally, a model of the accumulation of SMP in anaerobic systems that incorporates the production and release of ECP into the bulk liquid was proposed. The model predicted relatively well the concentration of soluble species both at steady-state, and during the transient conditions of organic and hydraulic shock loads.

ASSUNTO(S)

post-treatment anaerobic treatment effluent characterization smp tratamento anaeróbio caracterização de efluentes soluble microbial products residual cod compostos microbianos solúveis biodegradability and toxicity engenharia quimica dqo residual

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