Industrial human activity has led to the release of substantial amounts of heavy metals into the environment. Contamination of water with heavy metals such as lead, cadmium, copper, zinc, chromium, or nickel represents a serious problem. As part of the circular economy, it is appropriate to use biowaste from agriculture, fisheries, and the timber industry as biosorbents. In this literature review, the potential of using these biowaste groups as biosorbents for metal removal is presented. This biowaste is characterized by the presence of carboxyl, hydroxyl, carbonyl, amide, amine, sulfydryl, and other groups on their surface, which form complexes and chelates with metals present in water. Biosorption seems to be a potential alternative to conventional technologies for removing or recovering heavy metals from water or wastewater, which are uneconomical and generate additional waste. The paper demonstrates that harnessing the potential of biowaste to remove metals is beneficial to the environment as they can solve the problem of incineration and realise recycling that meets the circular economy. Although the choice of a suitable biosorbent for the removal of a particular metal involves a lot of research, the high biosorption efficiency, low cost, and renewability justify their use.

Purification of leachates is currently a big challenge due to their high variability in composition and amount. The complexity of the medium, namely leachates, makes new solutions highly sought after and finds the existing ones in need of optimization. The effects of ultrasound pretreatment (20 kHz, 12 µm) on biological treatment of landfill leachates in the form of processes carried out in two sequencing batch reactors were investigated. The experiment was divided into two stages. In the first stage, leachate was treated by an ultrasonic field at different sonication times (0.5, 1, 3, 5, 10 and 15 min). Next, leachates with and without conditioning were combined with municipal wastewater in the following ratios: 5, 10, 15 and 25% v/v. For optimal processing time (3 min), 16% removal of COD was achieved. In turn, the BOD5/COD ratio was 0.3, which is higher by approximately 270% than that of the non-conditioned sample. Further elongation of sonication time did not significantly affect both parameters. Also, pretreatment of leachate resulted in a maximum increase noted in the study of specific oxygen uptake rate and dehydrogenase activity of approximately 21 and 2 times compared to the non-conditioned sample. The implementation of a pretreatment step prior to the biological treatment was shown to result in higher pollutant removal efficiency. Depending on the share of leachates in the mixture, the removal enhancements of BOD, COD, and ammonium nitrogen for conditioned samples ranged from 6–48.5%, 4–48% and 11–42%, respectively. Furthermore, pretreatment of leachate allows for an increased (by up to 20%) share of leachate volume in the influent stream entering the reactor, while maintaining the quality of effluents in accordance with national regulation requirements. However, in scenarios without pretreatment, the leachate ratio cannot exceed 5% of the total wastewater due to poor quality of the effluents. The operational cost of ultrasound pretreatment of leachate was 22.58 €/(m3·g removed COD).

The commonly application of nanoparticles (NPs) in commercial and industrial products inevitably increases their release into the natural environment which poses a threat to human health and ecosystems. A recent study of nanoparticles in wastewater treatment showed that most NPs are retained in the equipment used for biological wastewater treatment. The aim of the study was to determine the effects of silver nanoparticles (Ag NPs) on wastewater treatment in the SBR bioreactor. The effluent from the SBRs was analyzed for total organic carbon (TOC), suspended solids (SS), pH and total silver. Microbial observations of activated sludge were made and, on this basis, the Madonia biotic index was specified. After nanoparticles were added, the composition of microorganism communities of the activated sludge changed, and the largest community was the one of creeping ciliates. The efficiency of the effluent treatment measured by the concentration of TOC removal showed that Ag NPs were found to have remarkable effects on TOC removal in the SBR. The obtained results showed that purified wastewater included a low concentration of Ag nanoparticles. The main removal pathway of Ag NPs was via sorption as well as possible aggregation and sedimentation onto the sludge.

Abstract:The article investigated the effects of ultrasound pretreatment on biological treatment of landfill leachate. Leachates with and without conditioning were combined with municipal wastewater at different ratios. The study showed that the implementation of a pretreatment step prior to biological treatment not only results in higher pollutant removal efficiency but may also allow for an increased leachate volume share in the influent stream entering the reactor by up to 20% (quality of effluents meets national regulation requirements) which in scenarios without pretreatment cannot exceed 5% due to poor quality of the effluents.