Temporal dynamics and performance association of the tetrasphaera-enriched microbiome for enhanced biological phosphorus removal

Background

Phosphorus (P) eutrophication and P mineral resource depletion are increasingly serious global problems. Wastewater treatment plants (WWTPs) are both the sink and source for P. The bioprocess known as enhanced biological phosphorus removal (EBPR) can effectively promote P removal and recovery in WWTPs. It relies on a specific microbial functional guild called polyphosphate-accumulating organisms (PAOs). Recently, Tetrasphaera PAOs have gained increasing attention due to their prevalence in global WWTPs as both important contributors to P removal and potential reservoirs for P recovery. However, only a few studies have reported Tetrasphaera-enriched microbiomes that were fed amino acids as a sole carbon source. The enrichment strategy, process, and key biotic and abiotic factors are unclear, hindering the in-depth study of Tetrasphaera PAOs for optimizing the P removal and recovery in WWTPs. To fill above knowledge gaps, this study proposed and applied an enrichment strategy featuring intricately designed multi-carbon sources amended with low dosage allylthiourea to build a Tetrasphaera-enriched EBPR microbiome, and explored the associations between microbiome dynamics and treatment performance during the microbiome establishment process.

Experiment design

The top-down strategy including four stages to selectively enrich Tetrasphaera PAOs based on the top-down approach was designed. In stage I (days 0–73), the multi-carbon sources (containing amicase, glucose, and sodium acetate) and periodic operational conditions (anaerobic/aerobic alternations) were designed as the selective tactics to conduct the initial enrichment. In stage II (days 74–120), 1 mg/L allylthiourea was introduced to facilitate enrichment by suppressing nitrification. In the stages III (days 121–127) and IV (days 128–170), a transient shock with a high dosage of allylthiourea (5 mg/L) was applied to investigate the effect of allylthiourea dosage on the Tetrasphaera-enriched microbiome. During the 170-day reactor operation, the treatment performance and microbiome temporal dynamic were monitored, and the P recovery potential of the Tetrasphaera-enriched microbiome was evaluated.

Major results and conclusions

The established microbiome showed enhanced nutrient removal (P removal rate ~85% and N removal rate ~80%) and increased P recovery (up to 23.2 times) compared with the seeding activated sludge from a local full-scale WWTP. The supply of 1 mg/L allylthiourea promoted the coselection of Tetrasphaera PAOs and Microlunatus PAOs and sharply reduced the relative abundance of both ammonia oxidizer Nitrosomonas and putative competitors Brevundimonas and Paracoccus, facilitating the establishment of the EBPR microbiome. The high allylthiourea dosage (5 mg/L) showed a negative effect on the Tetrasphaera-enriched microbiome, which could cause ammonia accumulation and disturbance in the microbial community. Based on 16S rRNA gene analysis, a putative novel PAO species, EBPR-ASV0001, was identified with Tetrasphaera japonica as its closest relative. The microbial interaction and niche patterns revealed in the co-occurrence network of the Tetrasphaera-enriched microbiome were associated with the dynamics of the removal efficiency of nitrogen and phosphorus rather than organic carbon. In addition, the correlation nexus between microbial community, environmental variables, and EBPR performance supported that 1 mg/L allylthiourea could be the key abiotic factor for Tetrasphaera-enriched microbiome establishment. This study provides new knowledge on the establishment of a Tetrasphaera-enriched microbiome facilitated by allylthiourea, which can be further exploited to guide future process upgrading and optimization to achieve and/or enhance simultaneous biological phosphorus and nitrogen removal from high-concentration wastewater.