Municipal wastewater treatment plants (WWTPs) receive increasing pressure because of the high energy consumption. To address this issue, various partial nitritation-based anammox (PN/A) processes were developed owing to their significant economic benefits, by which the operational costs could be cut by 85% compared to the currently employed nitrification/denitrification process. However, there are no successful engineering projects in treating low-strength municipal wastewater so far. The main bottleneck is the difficulty in effectively suppressing nitrite-oxidizing bacteria (NOB), which leads to insufficient nitrite to maintain anammox activity resulting in high effluent nitrate concentrations.
We proposed a novel Sidestream Enhanced Mainstream Anammox (SEMA) process for energy-efficient municipal wastewater treatment. As displayed in Figure 18, organics in raw wastewater are recovered in A-stage, its effluent is fed to PN/A reactor, and a small portion of A-stage effluent is introduced to sidestream nitritation reactor along with centrate to achieve an efficient nitrite production. These two streams are then transferred to downstream anammox reactor together with a small portion of raw wastewater providing organics to enhance denitrification for in-situ nitrate removal. Assuming the nitrogen load of sidestream wastewater is 20% of that in municipal wastewater and a nitrogen removal efficiency (NRE) of 60% is achieved in the PN/A unit, nitrogen mass balance analysis indicated a low effluent total nitrogen (TN) concentration of 5.1 mg N/L could be achieved.
Multiple benefits could be achieved by the SEMA process in terms of economy, effectiveness, and efficiency, and the long-term stability and a suitable effluent quality could be guaranteed with an easy control. It thus has a great potential in engineering application. In contrast to the generally accepted viewpoint that sidestream wastewater needs to be treated separately, the beneficial role of integrating sidestream treatment in facilitating mainstream anammox should be recognized. Technology feasibility and economic viability of the proposed SEMA process will be further verified.