Artificial mixing and phosphorus inactivation methods using aluminum compounds are among the most popular lake restoration methods. Długie Lake (Olsztyńskie Lakeland, Poland) was restored using these two methods. Primarily, P precipitation and inactivation methods significantly increased the sorption properties of Długie Lake bottom sediment. Fifteen years after the termination of the restoration procedure, the alum-modified “active” sediment layer still has higher P adsorption abilities, which can limit P internal loading. Relatively low amounts of phosphates in the near-bottom water of Długie Lake, even in anoxia, as well as the fact that the assessed maximum sediment P sorption capacity is still higher than NH₄Cl–P (labile P) and BD–P (Fe-bound P) sum (“native exchangeable P”), confirm that hypothesis. Among the tested P adsorption models for the sediment, the double Langmuir model showed the best fit to the experimental data (the highest R² values). This may indicate that phosphorus adsorption by the tested sediments most likely occurs through phosphate binding at two types of active sorption sites. P adsorption by the studied lake sediment during experiments was significantly connected to aluminum content in sediment. The research into the adsorption properties of sediment can be used as a tool for the evaluation of lake restoration effects.

Lake Ełk as an important element of the urban landscape is associated with tourism and active recreation and because of it with the economy of the town. Since 1999 the renovation method with the use of artificial aeration with simultaneous phosphorus inactivation and also as a biological filter – BIO-HYDRO structures were applied on the lake. This process was lasting 10 years and brought only a short-term improvement. At the same time, the shores of the lake were managed to develop of lake tourism: beach, swimming pool, tennis courts, a promenade, and two a water equipment rentals. The illuminated fountain, the road bridge and well – developed catering – accommodation base were made as well.

The research presented in this work concerns the potential aluminum load of soft-water lake ecosystems as a result of performing chemical reclamation works. On a semitechnical scale, different doses of PAC-type aluminum coagulant (polyaluminum chloride) were tested. The required doses of coagulant (on average, 11 mg Al/L) were determined based on the amount of phosphorus that is bioavailable in the lake ecosystem. The research covered the lake water, near-bottom and interstitial water, and bottom sediments of five lakes with low alkalinity (0.4–2.5 meq/L) and low calcium contents (5–35 mg Ca/L). The experiments were conducted in situ for 2 years using mesocosms with a volume of approximately 20 m³. The effectiveness of the flocculation and sedimentation processes of coagulant flocs was closely related to changes in water pH caused by acidic coagulant application, and the corresponding transformation level ranged from 39.8 to 99.8%. In the waters of these lakes, where the alkalinity did not reach 1 meq/L, the coagulant used in doses adequate for intensive full-scale projects caused high water pollution with dissolved aluminum fractions (from 0.05 ± 0.01 to 4.67 ± 1.32 mg Al/L). In all lakes, the penetration of dissolved aluminum into the interstitial water of the bottom sediment was limited to the first 5-cm layer. After the application of coagulant, the aluminum content in the bottom sediments significantly increased in proportion to the amount of the PAC used (by 12–96% in terms of a 5-cm surface layer of sediment). Within 2 years of the research, solid fractions (flocks) of the coagulant moved to a depth of 5–10 cm below the bottom level. Due to high release rates of aluminum from the applied aluminum treatments, modifications to the treatment protocols are needed in soft-water lakes.

This study compared the performance of powdered (PAC 200-1Wi and PAC 200-C303) and granular (GAC 10-GAC and GAC 10CO) activated carbons in organic removal from landfill leachate using the UV₂₅₄ and UV₂₈₀ indices, in addition to chemical oxygen demand (COD) and dissolved organic carbon. Process efficiency increased to the greatest extent when the range of carbon doses was 2–3 g/L (PAC 200-1Wi) and 2–10 g/L (both GACs). In these ranges, an increase in PAC dose of 1 g/L gave an increase in COD and UV₂₅₄ removal efficiency of 19.1 and 15.4%, respectively, with GACs, the increase was 4.0–4.3% COD and 5.4–6.0% (UV₂₅₄). Higher doses proved less efficient because the high consumption of carbon yielded 8–10 times lower increase in process efficiency than lower doses. Organics adsorption followed pseudo-second-order kinetics. With PACs, equilibrium was reached in 30 min; whereas, with GACs, equilibrium was reached in 48 h. Q_e for PACs was 2–3 times higher than GACs.