Summary:

Industrial effluents have currently constituted the main portion of a total volume of generated sewage, however a tendency to diminish their quantity has been observed. Treatment of specific sewage faces serious technological problems due to the special character of production in the manufacturing plants, which affects the irregularity and amount of pollutants. Considerable quantitative and qualitative variability of the generated sewage is perceivable even at the plants with the same profile of production. Therefore, it is necessary to identify precisely the properties of effluents produced not only by the same branches of industry but even by single factories. Considering the food sector enterprises, the least amount of literature data is available on physicochemical properties of effluents generated by confectionery industry. Therefore, the study aims to characterize the effluents produced by confectionery factories and compare them with the properties of sewage from other food manufacturing plants. The main emphasis was put on the analysis of the results of research on confectionery effluent treatment in a model bioreactor with activated sludge. The main characteristics of sewage generated by confectionery factories are considerable fluctuations of pollutant quantities, which is a frequent cause of observed operational problems with the treatment plant process line. Compared with other food industry enterprises (such as dairy plants, slaughter houses, breweries or sugar mills) confectionery effluents reveal smaller pollutant contents but their fluctuations in the outflow are similar. On the other hand, in comparison with domestic sewage they contain slightly greater concentrations of organic impurities, suspended matter and total nitrogen. The above mentioned parameters of the discussed sewage point to their potential joint treatment. Mixing confectionery effluents with domestic sewage would reduce the irregularity of concentrations and loads of impurities and at the same time it would positively affect their balance in the inflow to a treatment plant. The analyzed sewage may be regarded as susceptible to biological decomposition, since total percentage of degradable organic substance is 92% of total COD and is higher than registered in municipal wastes, where it ranges from 75-80% of total COD. Biodegradable organic particulate fraction in confectionery effluents constitutes about 20% of total COD, which in comparison with domestic sewage, where this fraction share reaches 50%, is a definitely lower value. Technological system applied for confectionery effluent treatment was a two step biological reactor with activated sludge adapted for enhanced removal of nitrogen compounds from sewage. The technological line of model treatment plant comprised the following elements: denitrification chamber, bioreactor composed of two concentrically placed chambers, the internal nitrification chamber and the external one functioning as secondary settlement tank. External and internal sludge recirculation was used in the analysed system. Conducted research and obtained results show that the applied technological system may guarantee a sufficient reduction of impurities from sewage, meeting the requirements of sewage effluent disposal consent granted to the enterprise. The experimental results showed a probability of not exceeding the analysed pollution indices in the outflow from the secondary settlement tank: 100% for BOD₅, 100% for COD, 100% for total suspended solids, 72.5% for total nitrogen and 100% for total phosphorus. Technological parameters of the bioreactor at which the most satisfactory results were obtained are as follows: oxygen concentration in the aeration chamber: 2.0mgO₂ ·dm^-3, reaction in the aeration chamber: 8.4 – 8.8, sludge age:6-11 days, sludge pollutant loading: 0.2kg BOD₅·kgsm^-1·d^-1, sludge index: 120ml ·g^-1 and degree of sludge recirculation: 100 – 240%. Despite the satisfactory results of treatment, the analysed system did not work steadily because of highly variable physicochemical properties of raw sewage. This pertained mainly to nitrogen compounds. Occasional sudden shock loadings of the activated sludge with ammonium nitrogen caused changes in microorganism population, which in consequence led to a decrease in nitrification rate and caused problems with nitrification. Microbiological analysis of the activated sludge revealed that it was stabile and in good condition despite problems with its bulking caused by filamentous bacteria