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Batch toxicity and biodegradability of two azo dyes (Siriusgelb and Siriuslichtbraun) has been investigated. It was found that the former azo dye was significantly less toxic to methanogenic sludge than the latter one (IC50 are equal to 3.55 and 0.41 g COD/l, respectively). Neither of the azo dyes was biodegradable under aerobic conditions but both dyes were readily decolourised and slowly mineralised in anaerobic environments. In order to optimise the treatment strategy, the anaerobic and aerobic phases were combined into one single unit called the anaerobic-aerobic hybrid reactor. The performance of this innovative reactor was tested with a synthetic wastewater containing Siriusgelb and ethanol at 30°C and 56% removal of azo dye COD was achieved at volumetric load of 0.3 g azo dye COD/l/day. The effluent COD content could be attributed to the presence of non-biodegradable autooxidation products of Siriusgelb breakdown intermediates. A continuous biomineralisation of 2-aminobenzoic acid (2-ABA) – intermediate of the anaerobic decomposition of Siriuslichtbraun – was studied in a UASB reactor at 30°C. A high (>90%) removal of 2-ABA was achieved under volumetric loads of 1.5 g 2-ABA COD/l/day. However, a further increase in volumetric load led to a decrease in 2-ABA removal, probably due to low attachment ability of the bacteria responsible for primary decomposition of 2-ABA.

The operating performance of a single and two (in series) laboratory upflow anaerobic sludge-bed (UASB) reactors (2.7-L working volume, recycle ratio varied from 1:1 to 1:18) treating diluted wine vinasse was investigated under psychrophilic conditions (4-10 degreesC). For a single UASB reactor seeded with granular sludge, the average organic loading rates (OLRs) applied were 4.7, 3.7, and 1.7 g of chemical oxygen demand (COD)/(L.d) (hydraulic retention times [HRTs] were about 1 d) at 9-11, 6 to 7, and 4 to 5 degreesC, respectively. The average total COD removal for preacidified vinasse wastewater was about 60% for all the temperature regimes tested. For two UASB reactors in series, the average total COD removal for treatment of non-preacidified wastewater exceeded 70% (the average OLRs for a whole system were 2.2, 1.8, and 1.3 g of COD/[L.d] under HRTs of 2 d at 10, 7, and 4 degreesC, respectively). In situ determinations of kinetic sludge characteristics (apparent Vm and Km) revealed the existence of substantial mass transfer limitations for the soluble substrates inside the reactor sludge bed. Therefore, application of higher recycle ratios is essential for enhancement of UASB pretreatment under psychrophilic conditions. The produced anaerobic effluents were shown to be efficiently posttreated aerobically: final effluent COD concentrations were about 0.1 g/L. Successful operation of the UASB reactors at quite low temperatures (4-10 degreesC) opens some perspectives for application of high-rate anaerobic pretreatment at ambient temperatures.

One possible solution for sustainable utilisation and treatment of diluted manure streams is preliminary separation of the solid and liquid fractions followed by separate biological treatment of both fractions. This approach was the starting point of a joint Russian-Dutch project: “The Development of Biotechnological Methods for Utilisation and Treatment of Diluted Manure Streams” (1996-1998). This paper describes the most important results of the project. The UASB process was found to be suitable for the pre-treatment of the liquid fraction of various types of manure using a lab-scale experimental set-up. The maximum organic loading rate (OLR) applied was approximately 12 g COD/1/day for hen or pig manure and 6 g COD/1/day for cattle manure using a hydraulic retention time (HRT) of about 1 day. The total COD reduction under these conditions was about 75% for the hen or pig manure and 42% for the cattle manure. The effluents obtained in this step can be used as liquid fertilisers (if possible) or should be post-treated to meet standards for discharge or reuse. Intensive composting can efficiently treat the solid manure fraction. Experiments at a pilot scale level with the solid fraction of hen manure showed that various amendments (peat, straw, sawdust) could be used for the production of composts having an elevated NPK content, reduced levels of Clostridia and faecal coliforms, vital weed seeds and the absence of Salmonella and helminth eggs.