Advances in Biogas Technology - Biotechnology in China: Biofuels and Bioenergy - page 135

AnMBR is highly cost-effective, because it needs no aeration; instead methane and
biological resources can be recovered in this process. However, AnMBRs have
much stricter requirements on their operating conditions. The main operational
parameters include: volume organic load of 2.9-50 kg COD/(m 3 d), HRT of 12 h,
SRT of 6-300 day, MLSS of 8-50 g/L, transmembrane pressure of 100-500 kPa,
membrane L/(m 2 flux of 18-150 h), and COD removal of 85-97%. The

side-stream-type AnMBR has been primarily adopted in practice.
Wang et al. [ 36 ] designed an AnMBR to treat the actual sewage from Tsinghua
University. In this system, additional fine fiber filling was packed at the top of the
anaerobic sludge bed to prevent sludge washout, and hollow fiber membranes were
set in the lower part of reactor. The membrane uses polyethylene material, and has an
aperture size of 0.03 lm and filtering area of 0.3 m 2 . The results showed that the
system could withstand severe organic load fluctuation. When the organic load
changed dramatically from 0.5 to 12.5 kg/(m 3 d), the average effluent COD remained
less than 20 mg/L, and the total COD removal was about 97% with no SS detected in
the effluent. Guan et al. [ 37 ] used a two-phase AnMBR to treat organic wastewater
polluted by industrial starch and grape bran. The COD and SS concentrations were
1,500-1,700 mg/L and 1,000-4,000 mg/L, respectively. The acidogenic reactor and
methane-producing reactor were placed in a 35 C incubator, while the membrane
separation unit was set between the two-phase reactors and operated under ambient
temperature. A polypropylene hollow fiber membrane with an aperture size of
0.1-0.49 lm was adopted. A high COD removal of above 95% and SS removal of
over 92% were achieved in this system. In addition, the introduction of a membrane
unit significantly enhanced operational stability of the two-phase anaerobic nitrifi-
cation system. He et al. [ 38 ] treated high organic-concentration food wastewater
using an AnMBR, which consists of a complete-mixing anaerobic biological reactor
and a plate-frame ultrafiltration membrane module. Polyether sulphone was used as
the membrane material. This system removed 80-90% of the COD even at a high
COD load of 2.3 kg/(m 3 d). The removals of SS, chroma and bacteria reached as high
as 100, 98 and 99%, respectively.

3.2 Dry Digestion Technology

Dry digestion is an innovative technology that allows direct biogas production
from solid-state organic wastes. The content of solid organic wastes can reach
35%, which is considerably higher than that in traditional anaerobic digesters
(8%). Normally, a solid organic waste content of 20% is more suitable. Dry
digestion can not only improve gas production rate and efficiency per tank volume,
but also simplify the operation and reduce the cost. The digested products can be
directly utilized as fertilizers or soil conditioners without dewatering. With all
these advantages, the dry digestion technology is attracting increasing interest for
the treatment of municipal solid waste and lignocellulosic waste [ 39 ].