With the advantages of efficient removal, low cost and simple operation management, pond-ditch circulation systems (PDCSs) has been proved to be a promising technology for rural wastewater treatment. However, the biological phosphorus (P) removal processes remain elusive.    

Researchers from the Wuhan Botanical Garden and the Institute of Hydrobiology investigated P removal performance, different forms of P in sediments, associated enzyme activity, bacterial diversity and communities of PDCSs for rural wastewater treatment lasting two successive months. 

In this study, the researchers demonstrated that PDCSs could effectively reduce the contents of P in rural wastewater (77.8%–97.4%). The activities of polyphosphate kinase (PPK) and exopolyphosphatase (PPX) increased from day 14 to day 30 and then declined, and tightly linked with most sediment properties, such as sediment total phosphorus (STP), sediment inorganic phosphorus (SIP), P bound to Al/Fe/Mn oxides and hydroxides (NaOH-P), P associated with Ca (HCl-P), and organic matter (OM).   

Moreover, Bacillus and Clostridium, and Geobacter and Arthrobacter, were likely the dominant P-accumulating groups participating in biological P removal of ponds and ditch, respectively.  

Microbial community structures from two ponds of PDCS taken at day 30 were more affected by Temperature (W-temp), TP, dissolved oxygen (DO), NaOH-P, and OM than those in the ditch. 

Furthermore, the direct effects of STP on PPK activity in PDCSs were slightly lower than their indirect effects mediated through variations in the relative abundance of bacterial taxa. W-temp, DO, and OM affected PPK and PPX activities in PDCSs via regulating the relative abundance of bacterial taxa and STP.   

These findings highlight that the feedback between water quality (temperature and DO), edaphic conditions (OM and STP), and the relative abundance of bacterial taxa plays an important role in controlling biological dephosphorization process in PDCSs. 

Relevant research results have been published in Science of the Total Environment entitled "Environmental factors and microbial communities jointly regulate biological dephosphorization process in pond-ditch circulation systems (PDCSs) for rural wastewater treatment". 

This study was supported by grants from the National Natural Science Foundation of China.  

A schematic diagram of Poly-P metabolism pathway in PDCSs microorganisms (Image by MA Lin)