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Abstract. The Wastewater Treatment Plant (WWTP) 'Swarzewo' plays a special role in the protection of coastal waters of the Baltic Sea area and the management of solid wastes in the region. This paper discusses several options implemented in the WWTP area in order to achieve sustainability. The first one was the inclusion of WWTP into municipal waste management plan to increase the biogas production and to reduce volume of organic waste in the region. Nowadays, daily production of about 2000 m 3 of biogas is gained. The energy balance shows a considerable benefit from the co-fermentation of sludge with municipal organic wastes. The next goal was to obtain a favorable economical balance of energy and high level of pollution reduction. The last one was the involvement of local communities in a conscious segregation of waste 'at source'. For the purpose of this paper bio-energy production, nutrient elimination, composting, and research, have been selected as indicators of sustainable development. Furthermore, in this study the methods of nutrient recovery from wastewater were explored. Struvite precipitation and compost production were presented as an example of nutrient elimination with 'end of waste' production. Depending on the struvite precipitation conditions, recovery of 4 Mg of phosphorous and 1,8 Mg of nitrogen is possible to obtain annually.

The article discusses the procedures of agricultural waste management in the context of the principle of maximum closed loop for organic compounds. The concept of regional agro-waste economy is presented taking into account existing technological solutions including agricultural biogas plants as well as biogas plants located at sewage treatment plants. The biogas potential for agricultural waste co-fermented with primary sludge of the ‘Swarzewo’ wastewater treatment plant was estimated.

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Removal of nutrients from wastewater with simultaneous recovery of phosphorus (P) and nitrogen (N) in the form assimilable by plants is possible by the precipitation of ammonium magnesium phosphate (struvite). This method benefits environmental protection but has not been widely implemented in Wastewater Treatment Plants (WWTPs). One of the reasons is the high costs of available technologies. The aim of the work is to investigate the low-cost methods of reduction and recovery of nutrients from wastewater. It involves the precipitation of struvite from phosphate-rich leachate from WWTP fermentation chambers. The reaction was carried out in the prototype of a simple horizontal reactor, ensuring the possibility of collecting sediment in the funnel. A cheap waste magnesium salt was used to precipitate the struvite, which significantly reduced the costs of its acquisition. The reduction of P exceeded 80% in most of performed tests in leachate waters. The precipitant removed from the reactor has the character of sludge with a significant degree of hydration (85%). After drying, it is a dusty powder with an average P content of 40% and a total N content of 8% and a trace of heavy metals. It was proposed to mix the obtained aqueous form of struvite sediments with compost produced from excessive sludge, without drying it. Studies have shown that one percent of struvite admixture in compost results in an increase of P and N content by 13% and 2.7%, respectively.

Significant quantities of pharmaceutical substances enter biological wastewater treatment plants, where they interact with activated sludge microorganisms. An example of a pharmaceutical commonly used is the non-steroidal anti-inflammatory drug diclofenac (DCF). The presence of high concentrations of DCF in wastewater can disrupt nutrient removal processes, which are highly sensitive to external environmental factors. This paper discusses the effect of high DCF concentrations (1.04 mg/dm3–12.5 mg/dm3; 0.25 mg/gTS–3.0 mg/gTS) on the efficiency of nitrifying, denitrifying and phosphate-accumulating organisms in the wastewater treatment cycle. The condition of the activated sludge was assessed on the basis of the oxygen and nitrogen uptake rates values and the ability to biologically remove phosphorus compounds from the wastewater. The effect of DCF on the ability of methane-forming bacteria to produce biogas in the anaerobic digester was also investigated. None of the biochemical reactions of activated sludge were inhibited at applied DCF concentrations. A 33% reduction in biogas production was observed at a DCF dose of 0.0391 mg/gTS. Slight deviations from the typical course of biochemical transformation of ammonium compounds were recorded at a DCF concentration of 3 mg/gTS of sludge. However, in the concentration range studied, no negative effect of DCF, on the operation of the activated sludge, was found.

The article discusses the problem of excessive growth of one-year filamentous algae, contributing to the disturbance of ecological balance in the Puck Bay. The aim of the study is to estimate the possibility of restoring this balance through the use of macroalgae as a co-substrate for biogas and fertilizer production in the regional biological wastewater treatment plant (WWTP). Effectiveness of biogas production from aquatic plants, including free-floating filamentous algae, was examined. Tests have shown that the biogas potential of seaweed constitutes the level of 162 m3/Mg of organic dry solid substances of algae. It was estimated that using the summer intense algal growth, removing 65,000 Mg of algae, 800,000 m3 of biogas can be obtained from the area covering the inner Puck Bay. After biogas conversion, 2,320 MWh of electricity and 2,100 MWh of heat energy could be produced. Harvesting free-floating algae enables the annual removal of 100-150 Mg of phosphorus and 200-400 Mg of nitrogen from Puck Bay and, thus, reduces the level of its eutrophication. Macroalgae management at a certain stage of growth also prevents the presence of algae on beaches and contributes to the improvement of fishing conditions and boosts the tourism value of the region.