Batch and continuous dosing of conventional and composite coagulation agents for fouling control in a pilot-scale MBR

Abstract

In the present study, conventional and composite, laboratory prepared coagulation agents were added in a fully automatic pilot-scale Membrane Bioreactor unit, both in batch-mode addition (‘Process I’) and in continuous-flow addition (‘Process II’) experiments, aiming to improve the overall process operability, i.e. as a fouling control method. A systematic effort was made to: i) correlate the recorded trans-Membrane Pressure with two novel, easily generated fouling indices (Ratio a and Ratio b) and ii) elucidate the relationship between the coagulant equilibrium concentration in the activated sludge and the optimal amount of coagulant added/L of incoming wastewater, by applying the corresponding mass balance equation. In both processes, the ranking trend among the optimal coagulants can be classified as: FO 4350 SSH<PSiCAFPAC-18-10-15<PAC A9-M, in increasing order of Soluble Microbial Products (SMP) removal, and as: PAC A9-M<PSiCAFPAC-18-10-15<FO 4350SSH, in increasing order of sludge filterability enhancement. Among the three coagulation agents, the cationic polyelectrolyte FO 4350SSH was identified as the optimal one, since its continuous-flow addition was found to cause the largest TMP decrease (almost 40%), at the optimal dosage of 0.16mg/L of incoming wastewater, which was 63 times lower than its equilibrium concentration in the bioreactor (10mg/L). The respective low values of Ratio b and the short-term nature of continuous-flow experiments (6days) indicate that the mitigation of reversible fouling was mainly responsible for this.