Rejane Helena Ribeiro da Costa

The recovery of extracellular polymeric substances (EPS) from activated sludge (AS) represents a promising strategy to transform wastewater treatment plants (WWTPs) into resource recovery facilities within a circular economy framework. In this study, EPS was extracted from an AS process in a full-scale WWTP, highlighting its catalytic and bioflocculant properties, which represent an innovation in the valorization of this biopolymer. The EPS was subsequently characterized in terms of polysaccharides, proteins, and enzymatic activities (amylase and lipase). The bioflocculation performance of the EPS was evaluated using activated sludge mixed liquor. Results showed that EPS recovery yields using 50 °C and 80 °C were 196.3 ± 38.2 mg EPS/g sludge and 283.5 ± 85.4 mg EPS/g sludge, respectively. Enzymatic assays confirmed amylase activity ranging from 100 to 350 U/g sludge according to the extraction temperature. Lipolytic activity (20 U/g sludge) was comparable to values reported in the literature for EPS from biological sludge. The addition of EPS significantly improved the sludge settling velocity (from 0.86 to 4.48 m/h) and the sludge volume index (from 118.6 to 35.5). However, EPS application also increased the resistance to filtration by 50% and reduced cellular respiration by approximately 40%. Overall, the findings demonstrate that EPS from activated sludge acts as an effective bioflocculant with relevant catalytic properties, highlighting its potential as a high-value biotechnological product while also pointing to operational challenges that require further optimization.

This study investigated the effect of magnetite nanoparticles (Np-magnetite) added to a pilot-scale sequencing batch reactor (SBR) treating domestic wastewater, to improve aerobic granular sludge (AGS) formation and the effects of granule disintegration. Np-magnetite additions (75 mg L⁻¹) were made during the start-up of the reactor and repeated after 100 and 170 days, when granule disintegration was observed. From the first Np-magnetite addition, SVI₅ was reduced from 1315 to 85 mL g⁻¹. The granular biomass was observed on the 56th day, when 57% of the granules presented diameters bigger than 212 µm. The 100-day disintegration episode disturbed the granular biomass, reducing the volatile suspended solids by 51%, increasing the SVI values to above 200 mL g⁻¹. Np-magnetite addition recovered all the granular biomass parameters to the values observed before disintegration. The treatment efficiency was stable during operation of the reactor for nutrients (52.8 ± 23.4% NH₄⁺–N; 54.5 ± 12.2% PO₄³⁻–P) and carbonaceous organic matter (71.7 ± 12.7% BOD₅; 77.5 ± 10.0% COD_t). Np-magnetite addition changed the microbial community of the granular sludge, analysed via high-throughput 16S RNA sequencing, and recovered the treatment efficiency previously disturbed by the disintegration processes. These results indicate the potential of Np-magnetite as an agent for sludge aggregation in an aerobic granular reactor.

Aerobic granular sludge (AGS) is a microbial biofilm self-aggregation, which is effective for nutrient and pollutant removal, through the development of dense microbial layers bound together with extracellular polymeric substances (EPSs). However, long start-up times and granule disintegration are still challenges ahead. An array of external additives, including ion chelating agents, sludge-based enhancers, and magnetic influence have been tested to overcome these barriers. The application of such additives may promote enhanced EPS production, neutralization of charges on the bacterial surface, acts as a core-induced agent, or as a bridge to connect EPSs and cell surfaces. Although additives may improve the granule formation without reducing treatment efficiencies, there are still environmental concerns due to the fate and toxicity of discharged excess sludge. This mini-review identifies an array of external additives and their mechanisms to improve granulation properties, and proposes discussion about the technical and economic viability of these additives. Key points • Additives reduce granulation time and repair granule disintegration. • Biopolymer-based additives fulfill technical and environmental requirements. • Sludge-based additives are cheap and in line with the resource recovery concept. • The need for environmental-friendly additives for aerobic granular sludge process. • External additives affect granular biomass size distribution.

The present study evaluated the phosphorus removal in a Sequencing Batch Reactor (SBR - 2,500L) used to treat the wastewater from an office building in two steps: phase I-Enhanced biological phosphorus removal (EBPR) and phase II-co-precipitation using FeCl₃ as precipitant. The raw sewage presented a high organic load variation ranging from 0.11 (phase I) to 0.66 (phase II) kgCOD.m^-3.d^-1. A better phosphorus removal performance was obtained during co-precipitation (from 19.0 to 1.2 mg.L^-1 = 93% of efficiency) compared with biological removal (from 15.6 to 9.0 mgL^-1 = 42% of efficiency). FISH analyses did not demonstrate a strong PAO inhibition; however, nitrifying and denitrifying organisms (NSO and PAE) showed a significant activity reduction during phase II. Therefore, the bench tests made to obtain the oxygen uptake rate (OUR) revealed a heterotrophic organisms activity significantly lower in phase II (46.8 mgDQO_T.L^-1) than phase I (211.8 mgDQO_T.L^-1), indicating metabolic inhibition. The co-precipitation processes enhanced phosphorus removal, bringing the SBR effluent into accord with state law requirements; however, the inhibitory effect of ferric chloride on microorganism activity was highlighted.

A full-scale anaerobic side-stream reactor (ASSR) for sludge reduction was monitored in terms of sludge production and compared with the previous conventional activated sludge configuration (CAS). A detailed solid mass balance was calculated on the whole full-scale plant to estimate the sludge reduction associated with the ASSR. The activity of the biomass, which undergoes alternation of aerobic and anaerobic conditions was investigated by the respirometric test. The ASSR promoted a reduction of heterotrophic biomass activity and the substrate consumption rate in the activated sludge implemented with ASSR (AS + ASSR) was 36% smaller than in the CAS period. The solid mass balance indicated a sludge reduction of 28%. During the 270-day operation, the observed sludge yield passed from 0.438 kgTSS/kgCOD in the CAS to 0.315 in the AS + ASSR configuration. The solubilization of COD, NH₄⁺-N and orthophosphate were verified under anaerobic conditions. The results suggest that the possible mechanisms of sludge reduction were the increase of the system sludge retention time (SRT) by ASSR addition, and the reduction in heterotrophic biomass activity added to the organic compounds hydrolysis.