Wastewater from the yeast production industry (WWY) is potentially harmful to surface water due to its high nitrogen and organic matter content; it can be used to produce compounds of higher commercial value, such as polyhydroxyalkanoates (PHA). PHA are polyester-type biopolymers synthesized by bacteria as energy reservoirs that can potentially substitute petrochemical-derived plastics. In this exploratory work, effluent from WWY was used to produce PHA, using a three-step setup of mixed microbial cultures involving one anaerobic and two aerobic reactors. First, volatile fatty acids (VFA; 2.5 g/L) were produced on an anaerobic batch reactor (reactor A) fed with WWY, using a heat pretreated sludge inoculum to eliminate methanogenic activity. Concurrently, PHA-producing bacteria were enriched using synthetic VFA in a sequencing batch reactor (SBR, reactor C) operated for 78 days. Finally, a polyhydroxybutyrate (PHB)-producing reactor (reactor B) was assembled using the inoculum enriched with PHA-producing bacteria and the raw and distilled effluent from the anaerobic reactor as a substrate. A maximum accumulation of 17% of PHB based on cell dry weight was achieved with a yield of 1.2 g PHB/L when feeding with the distilled effluent. Roche 454 16S rRNA gene amplicon pyrosequencing of the PHA-producing reactor showed that the microbial community was dominated by the PHA-producing bacterial species Paracoccus alcalophilus (32%) and Azoarcus sp. (44%). Our results show promising PHB accumulation rates that outperform previously reported results obtained with real substrates and mixed cultures, demonstrating a sustainable approach for the production of PHA less prone to contamination than a pure culture.

The increasing use of chemical fertilizers causes the loss of natural biological nitrogen fixation in soils, water eutrophication and emits more than 300 Mton CO₂ per year. It also limits the success of external bacterial inoculation in the soil. Nitrogen fixing bacteria can be inhibited by the presence of ammonia as its presence can inhibit biological nitrogen fixation. Two aerobic sludges from wastewater treatment plants (WWTP) were exposed to high ammonium salts concentrations (>450 mg L⁻¹ and >2 dS m⁻¹). Microbial analysis after treatment through 16S pyrosequencing showed the presence of Fluviicola sp. (17.70%), a genus of the Clostridiaceae family (11.17%), and Azospirillum sp. (10.42%), which were present at the beginning with lower abundance. Denaturing gradient gel electrophoresis (DGGE) analysis based on nifH genes did not show changes in the nitrogen-fixing population. Nitrogen-Fixing Bacteria (NFB) were identified and associated with other microorganisms involved in the nitrogen cycle, presumably for survival at extreme conditions. The potential use of aerobic sludges enriched with NFB is proposed as an alternative to chemical fertilizer as this bacteria could supplement nitrogen to the plant showing competitive results with chemical fertilization.

Conventional biological wastewater treatment plants are not generally designed for organic micropollutant removal. Nanofiltration removes these micropollutants, producing a concentrate stream which may be recirculated into biological treatment. This principle was investigated in batch experiments, testing two sources of sludges and two media combinations (wastewater with nanofiltration concentrate). Although responses of two inocula were different, under these experimental conditions, nitrification activity was not substantially inhibited by concentrate addition and even doubled when initial micropollutant concentrations reached 100 μg/L. Among the 13 micropollutants tested, nanofiltration effectively rejected bezafibrate, irbesartan and diclofenac (>96% rejection), increasing their concentrations by 30% in the batch experiments. At low concentrations (0–10 μg/L), atenolol, bezafibrate and sulfamethoxazole were removed the most (64 ± 3 to 83 ± 13%). Whereas, at higher concentrations (100 μg/L), the removal increase was +68, +64 and +41% for irbesartan, diclofenac, and venlafaxine for sludge A, and +114, +83 and +65% for sulfamethoxazole, diclofenac and irbesartan for sludge B, respectively. Amisulpride and carbamazepine were highly persistent to biodegradation, and atenolol and trimethoprim were mostly removed by sorption to biomass. These results indicate that enhanced removal of biodegradable micropollutants is possible and nanofiltration concentrates can be recirculated into the biological system without jeopardising the wastewater nutrient removal.