The occurrence of microplastics (MPs) in wastewater has been studied in the last years. The high efficiency of their removal from wastewater is linked to their transfer to the sludge. In this work, the effect of high-density polyethylene (HDPE) on aerobic digestion was evaluated and these MPs were monitored, characterizing them by three different techniques. Two parallel batch digesters were monitored. AD-Control (meaning Aerobic Digester) operated as a reference, with no external HDPE particles, whereas these polymeric fragments were introduced to the second aerobic digester (AD-HDPE) using ring pulls as microplastic support. FTIR, Raman spectroscopies and fluorescence analysis of these microparticles showed some relevant results that should be highlighted. Higher fluorescence appeared after 7 days in the digester. It coincided with an increase of active volatile suspended solids (AVSS) in the AD-HDPE, which means that an increase of the microbial activity took place. Despite the presence of HDPE particles in the sludge, the digester performance was not compromised. Besides, the HDPE particles did not affect the microbial diversity (Shannon index) of the bacterial community at the end of the experiment compared to the bacterial community of the aerobic digester control tank. Based on the analysis of the relative abundances of microbial taxa, it was concluded that HDPE had selective effects on sludge microbial community, increasing the relative abundance of Bacteroridota phylum.

Wastewater treatment often enables discharge into natural water bodies, but for effective reuse, further treatment is essential. Membrane processes provide a precise solution yet face limitations due to fouling and organic material adsorption, impacting their performance. This study focuses on synthesising ultrafiltration membranes using non-solvent-induced phase separation. These membranes are produced from a Polyethersulfone/N,N′-dimethylacetanamide (PES/DMA) solution with varying concentrations of three commercial powdered activated carbons (ACs). The membranes undergo comprehensive analysis, revealing different behaviours based on AC type and concentration in the active layer. Among the membranes, Norit R with 0.5 wt.% concentration exhibits the highest polyethylene glycol (PEG) rejection, with an impressive rejection index (R) of 80.34% and permeability coefficient of 219.29 (L·m⁻²·h⁻¹·bar⁻¹). AC-enhanced membranes display superior selectivity compared to non-doped PES membranes. This work highlights the significant influence of AC textural properties, specifically specific surface area, total micropore volume, and average micropore width, on membrane performance, particularly the rejection index.

The increasing presence of microplastics (MPs) in wastewater sludge raises concerns about their potential interference with anaerobic digestion (AD), a key process for energy recovery and sludge stabilization. This study investigated the impact of three common MPs, polystyrene (PS), polyethylene terephthalate (PET), and high-density polyethylene (HDPE), on the anaerobic degradation of a synthetic, rapidly biodegradable substrate under controlled batch conditions with the biomass from an anaerobic digester as inoculum. Biogas production, intermediate metabolic parameters, and microbial community dynamics were comprehensively assessed. The results showed a moderate inhibition of methane yield in the presence of MPs, with HDPE causing the most significant reduction (up to 24%) in biogas generation. PS exhibited the lowest impact, independent of the concentration added (0.5 and 1.0 g·L⁻¹). The microbial community structure demonstrated robustness, with Firmicutes and Bacteroidota maintaining dominance and methanogenic populations largely unaffected, except in the presence of HDPE. Raman spectroscopy indicated that none of the MPs underwent substantial structural degradation, but the subtle spectral shifts—particularly in PET—suggested the initial stages of physicochemical alteration. These findings offer new insights into the short-term resilience and adaptability of anaerobic microbiomes in the presence of MPs while revealing potential signals of process disruption.