Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 240

will continue to be popular since it produces methane that can be recovered and used for
energy. Solids concentrations up to 35% can be processed. In addition, less carbon dioxide
is produced in comparison to aerobic processes. This could become an important consid-
eration due to the reduction requirements of the Kyoto Protocol and international treaty
on global warming. This amendment to the United Nations Framework Convention on
Climate Change (UNFCCC) reafirms sections of the UNFCCC to reduce emissions of car-
bon dioxide and ive other greenhouse gases from countries that ratify this Protocol.
Solids from anaerobic digestion can be composted. Supernatants from the sludge often
have high organic contents and need to be treated further. Anaerobic digestion of MSW
organics is performed at solids concentrations of 4% to 10%. Higher concentrations must be
diluted. Gas production is 1.5 to 2.5 m 3 /m 3 reactor or 0.25 to 0.45 m 3 /kg of biodegradable
volatile solids. Retention times are approximately 20 days. Most reactors operate under
mesophilic conditions.
Aerobic digestion is a highly stable process that can be operated so that nitriication can
also occur. Because of aeration requirements, it is more suitable for small- and medium-
sized plants. Capital costs are less than costs for anaerobic digestion, and operation is
safer since there are no explosive gases produced. Supernatants are also of higher quality.
Thermophilic digestion is becoming increasingly popular due to pathogen destruction,
and low space requirements and high sludge treatment rates. As an example, International
Bio-Recovery Corp. (North Vancouver, BC) has developed a technology named autoge-
nous thermophilic aerobic digestion (ATAD) that converts organic waste (food waste, sew-
age sludge, and animal manure) in to single-celled protein organic fertilizer after 72 h.
7.4.2 Water Resources Management
As up to 90% of human sewage in developing countries is untreated, this is a growing
threat to the health of surface water and groundwater. The capacity of rivers to absorb
these contaminants without irreparable impairment of water quality is being exceeded.
A combination of regulations and consumer incentives is needed to remedy the situa-
tion. Infrastructures must also be improved to reduce leakage from water supply systems.
Since water quality monitoring is nonexistent in many countries, the impact of urbaniza-
tion on water quality and water ecosystems is largely unknown—a situation that must be
remedied.
The lack of clean water on the one hand and looding on the other hand are problems
that beset many cities worldwide. Development of dams upstream instead of policies
for water sustainability, has led to water supply problems for downstream cities. We
have previously discussed some of these problems in Chapter 3. Reuse of wastewater to
reduce contaminant discharges into water systems may also be beneicial. Introduction
of taxes or tax credits can also promote reduction in water use. Various other approaches
have been proposed by König (1999) including the use of plant roofs to adsorb roof run-
off with a combination of seepage or delayed drainage areas to allow rain water to return
to the groundwater. Roof runoff could also be collected for use in toilets as shown in
F i g u r e 7. 9.
In 2002, water consumption in Canada per capita was approximately 1500 m 3 per capita as
compared with less than 197 for Denmark. Through national efforts, a water conservation
program was introduced that included leak detection and repair, changing water taxation
and pricing, metering and water-saving devices, and public education. Water consumption
decreased from 1997 to 2006 by 18.5% (Danish Water and Wastewater Association, 2007).