Development of a membrane-assisted hybrid bioreactor for ammonia and COD removal in wastewaters

A new membrane-assisted hybrid bioreactor was developed to remove ammonia and organic matter. This system was composed of a hybrid circulating bed reactor (CBR) coupled in series to an ultrafiltration membrane module for biomass separation. The growth of biomass both in suspension and biofilms was promoted in the hybrid reactor. The system was operated for 103 days, during which a constant ammonia loading rate (ALR) was fed to the system. The COD/N-NH₄⁺ ratio was manipulated between 0 and 4, in order to study the effects of different organic matter concentrations on the nitrification capacity of the system. Experimental results have shown that it was feasible to operate with a membrane hybrid system attaining 99% chemical oxygen demand (COD) removal and ammonia conversion. The ALR was 0.92 kg N-NH₄⁺ m^-3 d^-1 and the organic loading rate (OLR) achieved up to 3.6 kg COD m^-3 d^-1. Also, the concentration of ammonia in the effluent was low, 1 mg N-NH₄⁺ dm^-3. Specific activity determinations have shown that there was a certain degree of segregation of nitrifiers and heterotrophs between the two biomass phases in the system. Growth of the slow-growing nitrifiers took place preferentially in the biofilm and the fast-growing heterotrophs grew in suspension. This fact allowed the nitrifying activity in the biofilm be maintained around 0.8 g N g^-1 protein d^-1, regardless of the addition of organic matter in the influent. The specific nitrifying activity of suspended biomass varied between 0.3 and 0.4 g N g^-1 VSS d^-1.