Biological nutrient removal enhancement using fermented primary and rotating belt filter biosolids.

This research compared the impact of two primary treatment options (i.e. primary clarification and rotating belt filtration (RBF)) on biological nutrients removal (BNR) process, using sludge fermentation liquid (SFL) as a carbon source. The liquid fraction of both fermented primary and RBF sludges comparably enhanced BNR. Despite the significant contribution of the unpurified SFL to the sharp increase in nutrient levels; i.e. 47%-64% (primary effluent; PE), and 45%-53% (RBF) of the soluble nitrogen and phosphorus loads; readily biodegradable COD and volatile fatty acids (VFAs) fractions of the combined feed increased significantly (2.5-6.1 times), compared to the original feed by additional SFL. Removal efficiencies in the reactors reached 57% (total nitrogen) and 92% (total phosphorus) after addition of SFL. Effluent nitrogen and phosphorus of the two reactors were close in the range of 15 ± 6 mg N/L, and 0.5 ± 0.3 mg P/L, respectively. Kinetics studies showed denitrification rates of 1.3, and 1.13 kg NO-N/m.d for primary effluent and RBF effluent-fed reactors, respectively. Phosphorus release rates were 11.7 and 9.7 mg PO-P/g VSS.h, for primary, and RBF effluents, respectively; showing 20%-22% lower rates in the RBF SFL. Incorporating experimental data into a plant-wide model for a 100 MLD facility receiving typical medium strength wastewater, showed that although primary treatment enhanced the biogas production by 96% (primary clarification) and 62% (RBF) trains; combined fermentation and anaerobic digestion was effective to enhance the biogas production by 59% on average, compared to the base scenario without primary treatment. Additionally, if primary clarification exists, then the addition of fermentation results in additional revenue of C$1890/d in the plant, considering additional revenue of C$2230/d due to VFA generation in contrast to only C$340/d loss due to the reduced methane production.