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Anaerobic Digestion of Aqueous Waste for Methane and Hydrogen
metabolism (<20%), a majority of mineral fertilizer can be substituted by using the
effluent for irrigation. Furthermore, energy and GHGs would be additionally saved
and the wastewater treatment costs will be reduced.
8.4.9 WASTeWATer TreATmenT
Cowan [93] points out that one way to reduce the emission of CO 2 and increase the
energy production from bioprocess technologies for wastewater treatment is to use
an integrated algae pond system (IAPS) to address the range of wastewater treatment
problems. The growth of algae requires the use of CO 2 that minimizes the emission
to the environment. Furthermore, the IAPS system produces a quality effluent suitable for irrigation, negates the food versus fuel debate, and reduces the demand for
fossil fuel-derived energy and fertilizers.
Ryan et al. [94] addressed the issue of wastewater treatment from ethanol-producing
biorefineries. They suggested that inorder to treat the effluent from these refineries efficiently and economically which meets the local requirements and minimizes the net water consumption, a process integration that (1) improves the existing
secondary (i.e., biological) treatment to maximize COD reduction, (2) incorporates
a tertiary “polishing” stage to remove color, and (3) uses the reverse osmosis membrane technology to recover process water would be desirable. They also showed that
the energy required for the secondary and tertiary treatment stages can be obtained
from biogas-derived power from the anaerobic digester. Thus, this type of an integrated approach of postbiological treatment of ethanol stillage can address the issues
of efficient refinery operation with minimum net water consumption.
8.4.10 dAiry eFFluenT
Energy generation potential from dairy effluent was recently evaluated by Desai
et al. [67]. India is the largest milk producer in the world (100 MMT). In an organized
sector, which produces only 30% of the total milk generated in the country, the
140  dairy processing plants generate a very significant amount of effluent that is
rich in organic waste. Desai et al. [67] described an anaerobic digestion system for
one dairy processing 100,000 l/day milk to generate biogas (biomethane) that can
provide energy for the aerators of the existing aerobic treatment system (mostly activated sludge system). The study presented the details of the anaerobic filter system. The 40 million liters of milk handled by the organized sector of milk industry
in India has potential of generating 11 MW power from methane produced by the
anaerobic digestion filter system.
8.4.11 ToFu WASTeWATer
Zheng et al. [62] examined the hydrogen production from organic wastewater from tofu
production by photo bacteria. While this is a very useful process, NH 4
+ , which is normally the integrant in organic wastewater, is the inhibitor for hydrogen production with
photo bacteria. They showed that the concentration of NH 4
+ at ≥2 mmol/l significantly
affected the hydrogen production of wild-type sphaeroides because NH 4
+ concentration