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Removal and fate of emerging organic micropollutants (EOMs) in municipal wastewater by a pilot-scale membrane bioreactor (MBR) treatment under varying solid retention times, Science of the Total Environment,

Retrofitting municipal wastewater treatment plants (WWTPs) to energy positive is a major challenge faced by many water utilities. Selection of innovative technologies to achieve retrofitting goals is critical for capital improvement programs in WWTPs. This paper aims to provide a statistical analysis method of unit energy consumption in conventional Finnish WWTPs, presenting Mikkeli WWTP as a case study. The average energy consumption at Finnish WWTPs was quantified as a mean of 0.49 kWh/m 3 with a standard deviation of 0.197. The statistical analysis showed that the total energy consumption in Finnish WWTPs are positively correlated with inflow rate and sludge production. However, the unit energy consumption decreases with increasing plant capacity. The energy benchmarking of Mikkeli WWTP confirmed the energy gap of 0.11 kWh/kg COD in electricity. The major energy saving potentials are attributed to secondary treatment, screening and grit removal, and influent pump stations. A plausible innovative retrofitting strategy comprising four emerging energyneutral or positive technologies is proposed to maximally harness the chemical energy content in wastewater: enhanced primary sedimentation, staged anaerobic fludized membrane bioreactor (SAF-MBR) with completely autotrophic nitrogen removal over nitrite process (CAN-ON), and co-digestion of sludge with organic food-waste. The net energy balance of emerging technologies showed a maximum energy saving potential of 1.26 kWh/kg COD, which could be sufficient to overcome the energy gap of Mikkeli WWTP, providing net positive energy surplus of 1.15 kWh/kg COD.

Relaxation and backwashing have become an integral part of membrane bioreactor (MBR) operations for fouling control. This study was carried out on real municipal wastewater to evaluate the influence of different operational strategies on membrane fouling at equivalent water yield. Four relaxation modes (MBR MBR, MBR and MBR) were tested to analyze membrane fouling behavior. For the optimization of relaxation modes, fouling rate in terms of trans-membrane pressure, hydraulic resistances and characteristics of fouling fractions were analyzed. It has been observed that cake layer resistance was minimum in MBR but pore blockage resistance was increased in all relaxation modes. Moreover, high instantaneous flux contributed significantly to fouling rate at the initial stage of MBR operations. Relaxation modes were also efficient in removing irreversible fouling to some extent. Under all relaxation modes, COD removal efficiency ranged from 92 to 96.5%. Ammonium and TP removal were on the lower side due to the short solids and hydraulic retention time.