Abstract
Ammonium stripping has gained increasing interest for nitrogen recovery in anaerobically digested effluents. However, the stripped effluents often still do not meet discharge standards, having high pH and residual pollutants. Constructed wetlands (CWs) are an easy to operate ecosystem and have a long history of application in treatment of wastewaters with extreme pH, such as acid mine drainage. However, knowledge of the mechanistic details involved in the use of CWs to treat high alkaline drainage, such as stripped effluent, is insufficient. This study explored the feasibility and effectiveness of using three sub-surface horizontal flow CWs to treat high alkaline stripped effluent (pH > 10). Two intensification strategies—intermittent aeration and effluent recirculation—were evaluated to enhance nitrogen depuration performance. The results show that the treatment of alkaline stripped effluent is feasible due to the high buffering capacity of the wetlands. Effluent recirculation combined with intermittent artificial aeration improves nitrogen removal, with 71% total nitrogen (TN) removal. Ammonia volatilization from the surface of the wetlands in high alkaline conditions only contributed to 3% of the total removed ammonium. The microbial abundance and activity had significant diversity for the various enhancement strategies used in the constructed wetland systems. Anammox is an important process for nitrogen removal in CWs treating alkaline stripped effluent, and possible enhancements of this process should be investigated further.
Highlights
There are many concerns about how to dispose of the large amounts of waste generated by pig farms
This study investigated the feasibility of using horizontal sub-surface flow constructed wetlands (HSFCWs) for post-treatment of anaerobically digested alkaline supernatant after an ammonium stripping process
The results demonstrated ammonia volatilization is in Constructed wetlands (CWs)-2 and CW-3, created by a longer aeration and effluent recirculation, theindicated main factors not the primary mechanism removing ammoniatime nitrogen in the present study,were which the increasing the ammonium removal
Summary
There are many concerns about how to dispose of the large amounts of waste generated by pig farms. Swine wastewater is a typical high strength wastewater containing high levels of organic matter, ammonia, and phosphorus [1]. Inappropriate treatment methods and indiscriminate discharge of swine wastewater could cause epidemic diseases and foul odours. Anaerobic digestion (AD) is considered an effective and economic technique for treating swine wastewater. It has the advantages of both energy recycling and reduced greenhouse gas emissions [2]. Large amounts of liquid digestate are often generated, from large- and super-large-scale biogas plants
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