Understanding the Impacts of Low-Energy and Low-Carbon Removal Technologies on Bio-P and Nutrient Recovery Processes

Biological nutrient removal (BNR) has long been recognized as the most viable way to remove N and P from wastewater. To increase economic and environmental sustainability, BNR is in need of technical advancements that reduce the energy and chemical consumption to allow better use of influent carbon (expressed as COD or BOD). This is especially true for water resource recovery facilities (WRRFs) that are required to meet both stringent effluent N and P limits. Shortcut N removal-based technologies are transforming biological N removal through improved energy and carbon efficiency and increased energy recovery potential through carbon sequestration (WEF, 2015). Biological P removal (bBio-P) plays a central role in recovering P from wastewater to meet the sustainability of future P resources, if integrated appropriately with subsequent extraction/purification steps (Yuan et al., 2012). However, bio-P becomes less stable when applied in conjunction with biological N removal processes due to i) competition with glycogen accumulating organisms (GAOs) (Liu et al., 1997); ii) introduction of nitrate/nitrite to anaerobic zone, thereby disrupting anaerobic carbon uptake (Hascoet et al., 1985); and iii) competition for carbon between heterotrophs and polyphosphate accumulating organisms (PAOs) (Guerrero et al., 2011). On the flip side, N removal via denitrification becomes carbon limited due to anaerobic uptake of carbon with bio-P especially for wastewaters with low carbon to nitrogen ratio (C/N).