Abstract
Design of ship sewage treatment systems that not only satisfy the use of small space on board but also meets International Maritime Organisation (IMO) latest emission standards is still a challenging problem for ship industry. This study provides a comparative disquisition between two different MBR reactors i.e, air-lift multilevel circulation membrane reactor (AMCMBR) and anaerobic/anoxic/aerobic membrane reactor (AOA-MBR) for domestic sewage treatment. The influence of pollutants volume loading rate (VLR) and C/N on effluent chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) and TN for marine domestic sewage was analyzed. The results revealed that AMCMBR showed better removal efficiencies for COD and TN than AOA-MBR. The volume of AMCMBR was only half of the AOA-MBR. In addition, high average value of mixed liquor volatile suspended solids (MLVSS)/mixed liquid suspended solids (MLSS) (i.e. 0.75) of AMCMBR indicated high biomass and good pollutants removal achieved by this reactor. An interesting phenomenon was found in the study regarding Urease activity for the two reactors. Urease activity for AMCMBR in different working conditions all exceeded AOA-MBR and there exist no clear difference of NR activities between AMCMBR and AOA-MBR except for low C/N ratio (i.e. 6 and 4). This phenomenon proved that AMCMBR has a greater performance for treating ship domestic wastewater.
Highlights
Ships discharge black and grey water directly into marine environment, which can bring excessive calamity to the marine ecosystem
The results demonstrated that anaerobic-microaerobic fixed biofilm (AMFB) reactor achieved the maximum 99 % COD removal efficiency at HRT of 24 h and almost all biochemical oxygen demand (BOD) was removed
3 Results and discussion 3.1 COD removal efficiency Two different membrane bioreactor (MBR) systems were investigated to explored organic carbon and nitrogen removal mechanism in ship wastewater under different pollutants loading
Summary
Ships discharge black and grey water directly into marine environment, which can bring excessive calamity to the marine ecosystem. Compared with the old IMO emission regulations, like MARPOL73/78 and MEPC.159(55), TN discharge standard is introduced for the first time in new regulation, which should be below 20 mg/L [5, 6]. MBR technology has been applied for wastewater treatment for many advantages, like biomass enrichment, ensured sludge-effluent separation, small footprint, easy manipulation of the hydraulic and sludge retention times (HRT and SRT) and excellent effluent quality [7,8,9]. Khan et al [12] used a laboratory-scale membrane bioreactor (MBR) for domestic wastewater treatment at two different pollutants volume loading rate (VLR). The results showed that NH4+-N, COD, and TN removals were ranged from 71 % to 97 %, from 78 % to 96 %, and from 20 % to 60 %, respectively. Hussain et al [14] developed an anaerobic-microaerobic fixed biofilm (AMFB) reactor to study carbon removal simultaneously
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