Utilizing anaerobic substrate distribution for growth of aerobic granular sludge in continuous-flow reactors.

The development of continuous flow reactors (CFRs) employing aerobic granular sludge (AGS) for the retrofit of existing wastewater treatment plants (WWTPs) using a continuous-flow activated sludge (CFAS) system has garnered increasing interest. This follows the worldwide adoption of AGS technology in sequencing batch reactors (SBRs). The better settleability of AGS compared to AS allows for process intensification of existing wastewater treatment plants without the difficult conversion of often relatively shallow CFRs to deeper AGS-SBRs. To retrofit existing CFAS systems with AGS, achieving both increased hydraulic capacity and enhanced biological nutrient removal necessitates the formation of granular sludge based on the same selective pressures applied in AGS-SBRs. Previous efforts have focussed mainly on the selective wasting of flocculent sludge and retaining granular sludge to drive aerobic granulation. In this study a pilot-scale CFR was developed to best mimic the implementation of the granulation mechanisms of full-scale AGS-SBRs. The pilot-scale reactor was fed with pre-settled municipal wastewater. We established metrics to assess the degree to which the proposed mechanisms were implemented in the pilot-scale CFR and compared them to data from full-scale AGS-SBRs, specifically with respect to the anaerobic distribution of granule forming substrates (GFS). The selective pressures for granular sludge formation were implemented through inclusion of anaerobic upflow selectors with a water depth of 2.5 meters, which yielded a sludge with properties similar to AGS from full-scale SBRs. In comparison to the CFAS system at Harnaschpolder WWTP treating the same pre-settled wastewater, a more than twofold increase in volumetric removal capacity for both phosphorus and nitrogen was achieved. The use of a completely mixed anaerobic selector, as opposed to an anaerobic upflow selector, caused a shift in EBPR activity from the largest towards the smallest size class, while nitrification was majorly unaffected. Anaerobic selective feeding via bottom-feeding is, therefore, favorable for the long-term stability of AGS, especially for less acidified wastewater. The research underlines the potential of AGS for enhancing the hydraulic and biological treatment capacity of existing CFAS systems.

Booster vaccination with Ad26.COV2.S or an Omicron-adapted vaccine in pre-immune hamsters protects against Omicron BA.2.

Since the original outbreak of the SARS-CoV-2 virus, several rapidly spreading SARS-CoV-2 variants of concern (VOC) have emerged. Here, we show that a single dose of Ad26.COV2.S (based on the Wuhan-Hu-1 spike variant) protects against the Gamma and Delta variants in naive hamsters, supporting the observed maintained vaccine efficacy in humans against these VOC. Adapted spike-based booster vaccines targeting Omicron variants have now been authorized in the absence of human efficacy data. We evaluated the immunogenicity and efficacy of Ad26.COV2.S.529 (encoding a stabilized Omicron BA.1 spike) in naive mice and in hamsters with pre-existing immunity to the Wuhan-Hu-1 spike. In naive mice, Ad26.COV2.S.529 elicited higher neutralizing antibody titers against SARS-CoV-2 Omicron BA.1 and BA.2, compared with Ad26.COV2.S. However, neutralizing titers against the SARS-CoV-2 B.1 (D614G) and Delta variants were lower after primary vaccination with Ad26.COV2.S.529 compared with Ad26.COV2.S. In contrast, we found comparable Omicron BA.1 and BA.2 neutralizing titers in hamsters with pre-existing Wuhan-Hu-1 spike immunity after vaccination with Ad26.COV2.S, Ad26.COV2.S.529 or a combination of the two vaccines. Moreover, all three vaccine modalities induced equivalent protection against Omicron BA.2 challenge in these animals. Overall, our data suggest that an Omicron BA.1-based booster in rodents does not improve immunogenicity and efficacy against Omicron BA.2 over an Ad26.COV2.S booster in a setting of pre-existing immunity to SARS-CoV-2.

Simultaneous growth and poly(3-hydroxybutyrate) (PHB) accumulation in a Plasticicumulans acidivorans dominated enrichment culture.

The wide variety of organic carbon to nitrogen and phosphorous ratios that are encountered in different wastewaters has a major impact on the poly(3-hydroxybutyrate) (PHB) accumulation potential of microbial communities. In this study we investigated the influence of the substrate composition in terms of the carbon to nitrogen (C/N) or phosphorus (C/P) ratio on the PHB accumulation performance. A multi-reactor set-up was used, enabling parallel experiments using identical inoculum of an enrichment culture dominated by Plasticicumulans acidivorans. In all experiments simultaneous PHB production and growth was observed. Generally, when trace amounts of growth nutrients were present the PHB production yield on substrate remained high for at least 12 h. Interestingly, from the carbon to nutrient ratio in the substrate, the PHB wt% could be accurately predicted in the accumulations. This study demonstrates that strict uncoupling of microbial growth and PHA accumulation is not required for achieving high cellular PHA-contents. Herewith the range of wastewaters that enable a cellular PHA content of 80 % or higher for at least 12 h is expanded to C:N and C:P-ratios exceeding COD:N of 26 gCOD:gNH4-N and COD:P of 511 gCOD:gPO4-P respectively.

PHA production from the organic fraction of municipal solid waste (OFMSW): Overcoming the inhibitory matrix.

Leachate from the source separated organic fraction of municipal solid waste (OFMSW) was evaluated as a substrate for polyhydroxyalkanoates (PHA) production. Initially, the enrichment step was conducted directly on leachate in a feast-famine regime. Maximization of the cellular PHA content of the enriched biomass yielded to low PHA content (29 wt%), suggesting that the selection for PHA-producers was unsuccessful. When the substrate for the enrichment was switched to a synthetic volatile fatty acid (VFA) mixture -resembling the VFA carbon composition of the leachate-the PHA-producers gained the competitive advantage and dominated. Subsequent accumulation with leachate in nutrient excess conditions resulted in a maximum PHA content of 78 wt%. Based on the experimental results, enriching a PHA-producing community in a "clean" VFA stream, and then accumulating PHA from a stream that does not allow for enrichment but does enable a high cellular PHA content, such as OFMSW leachate, makes the overall process much more economically attractive. The estimated overall process yield can be increased four-fold, in comparison to direct use of the complex matrix for both enrichment and accumulation.