(215o) Study On the Wastewater Reuse By Combination of Thermophilic Anaerobic Bioreactor With Forward Osmosis (FO)/Membrane Distillation (MD) Integrated Module

Study
on the wastewater reuse by combination of thermophilic
anaerobic bioreactor with Forward Osmosis (FO)/Membrane Distillation (MD)
integrated module

Zhang Jinsong,*
Kwan Zheng Xin Joseph, Goh Shuwen, Anthony Gordon
Fane^*

Singapore
Membrane Technology Centre(SMTC),Nanyang
Environment and Water Research Institute(NEWRI),Nanyang
Technological University,1 Cleantech Loop, CleanTech One, #06-08, Singapore 637141

*Corresponding author:  jszhang@ntu.edu.sg,
Tel: 65-65921835, Fax: 65- 67910756

Abstract

The organic loading and temperature
of wastewater from industries such as chemical, petroleum and pharmaceutical
are typically high. These characteristics make them potential candidates for
anaerobic bioprocess, which is able to process high strength wastewater and
generate energy in the form of methane. Due to the high temperature of
wastewater, applying thermophilic anaerobic digestion
has additional benefits over mesophilic digestion,
including a higher COD removal efficiency, faster degradation rate, and lower
methane solubility in wastewater. However, due to the incomplete degradation of
organics, the effluent from the anaerobic bioprocess usually contains a high
concentration of organics, which makes it difficult to reuse or dispose
according to the discharge standard.

In this study, a thermophilic
upflow anaerobic sludge blanket (UASB) combined with
the forward osmosis (FO)/membrane distillation (MD)
integrated
module has been demonstrated for the first time. The schematic
diagram of anaerobic bioprocess with FO/MD module is shown in Figure 1. The MD
process uses microporous hydrophobic membranes that
allow water vapour to pass through the dry pores,
while retaining the non-volatile organics and inorganics.
If the MD membrane was directly used to treat the UASB effluent, serious biofouling, scaling and wetting will occur. The FO process
is a membrane separation process which uses semi-permeable membranes that
allows water molecules to pass through while retaining bigger size solutes. The
driving force for water transport is an osmotic pressure gradient achieved by
using an osmotic ?draw solution' (DS). The FO/MD integrated module captures the
complementary advantages provided by FO and MD in a single step. By applying
the FO membrane process at the anaerobic bioprocess effluent side, nearly all
the organics and inorganics can be rejected at a low
fouling rate. This makes the FO membrane a perfect barrier to prevent MD
fouling and wetting. High temperature feed water will also mitigate the
concentration polarization effects usually observed in FO processes, resulting
in enhanced FO membrane flux. The draw solution is simultaneously regenerated in-situ
via the MD process, which completely retains the solute (such as NaCl) in DS while allowing water to diffuse across the
membrane into the permeate reservoir. The FO/MD module allows us to achieve a
product that is of distilled water quality and ready for reuse in a single
step.

Our experiments have shown that the
anaerobic bioreactor with FO/MD module had a high rejection for TOC, with a
calculated average of 99.55 ± 0.24 %. TOC levels in the permeate remained
fairly constant below 0.5 mg/L. Permeate conductivity was stable at 5 μS cm^-1 , which is comparable to the RO
permeate of wastewater reclamation. The average composition of the biogas
generated from the UASB process was found to be 67.4 % methane, with the
highest percentage being 83.6 %. Optimally, the bioprocess is able to produce a
maximum of 0.35 L methane for every gram of chemical oxygen demand (COD) that
is degraded.

Figure
1 Schematic diagram of side-stream UASB-FO/MD system

In conclusion, the integrated process
of combining the anaerobic bioprocess with the FO/MD module is a state-of-art
technology and a viable alternative to wastewater reclamation. This technology
appears to be particularly well suited for high-strength industrial waste
streams reclamation due to the potential to achieve high quality water product
with lower energy consumption and higher methane production.

Keywords: Thermophilic, Upflow Anaerobic Sludge Blanket (UASB), Forward Osmosis
(FO),  Membrane
Distillation (MD), FO/MD integrated module