Organic waste and the compost and vermicompost derived from it may have different agronomic values, but little work is available on this aspect of sewage sludge. A 75-day pot experiment with perennial ryegrass (Lolium perenne) as the test plant aimed to investigate the fertiliser value and organic matter replenishment capacity of digested sewage sludge (DS) and the compost (COM) and vermicompost (VC) made from it, applied in 1% and 3% doses on acidic sand and calcareous loam. The NPK content and availability, changes in organic carbon content and plant biomass, and the efficiency of the amendments as nitrogen fertilisers were investigated. The final average residual carbon content for DS, COM, and VC was 35 ± 34, 85 ± 46, and 55 ± 46%, respectively. The organic carbon mineralisation rate depended on the soil type. The additives induced significant N mineralisation in both soils: the average increment in mineral N content was 1.7 times the total added N on acidic sand and 4.2 times it on calcareous loam for the 1% dose. The agronomic efficiency of COM and VC as fertilisers was lower than that of DS. In the short term, DS proved to be the best fertiliser, while COM was the best for organic matter replenishment.

In this mini-review, we compiled various types of Polyvinyl-alcohol-based hydrogel construction recipes and methodologies, categorizing them based on their added materials or production methods for wastewater applications. This classification is vital for identifying recipes that require improvement in future research and for analyzing their practical parameters, such as durability, surface area, and cleaning efficiency. To evaluate their potential for long-term use, we examined the durability of these groups. D- and E-type media demonstrated notable durability, exhibiting lower degradation rates compared to A- and B-types. Additionally, we gathered information on the measuring technologies available for assessing the specific surface area of these media, a crucial parameter for both biological and adsorbent applications. Based on the available data, we recommend enhancing the quality and quantity of measurements by integrating and improving microscopic analysis and adsorption techniques. Furthermore, these hydrogels showed superior cleaning capacities compared to traditional carriers, with D- and E-types excelling in adsorption capabilities, while the C-type exhibited exceptional potential for biological treatment.

Traditional carriers play a major role in wastewater treatment worldwide due to their reliability, ease of production, well-established analytical methods, and strong treatment performance. Recent studies indicate that polyvinyl-alcohol-based microcarriers may surpass conventional media, as their smaller size, higher porosity, and increased specific surface area enable them to retain substantially more biomass within reactors. However, their practical application remains limited because fewer analytical methods and studies exist for these materials, largely due to their small dimensions and heat sensitivity, and their behaviour under industrial conditions—including their kinetics—has yet to be fully characterised and validated. This study aims to address these gaps by reviewing existing biomass measurement standards and highlighting their limitations when applied to microcarriers and by proposing alternative experimental approaches better suited for evaluating biomass on such sensitive yet high-capacity carriers. We present a set of experimental methods (still subject to further refinement) that demonstrate reliable performance with these materials, and to validate our approach, we quantified biomass in both in vitro systems and containerised-scale technologies, reaching up to 14 kg/m³ during winter and 8.7 kg/m³ in spring. Laboratory-scale experiments showed that both heterotrophic and autotrophic cultures can achieve high biomass levels of up to 21 kg/m³ and 16 kg/m³, respectively. Heterotrophs exhibited lower growth inhibition under shear stress, while autotrophs displayed a distinct shear-force niche around 0.09 µN within the reactor.