Environmental Engineering Reference
In-Depth Information
per day compared with low-income countries, which produce an average of 0.2 kg of haz-
ardous waste per person per day. In high income countries another 2 kg of waste is gen-
erated that is comparable to domestic waste. In low income countries hazardous and
nonhazardous wastes are not usually separated (WHO, 2011).
Pathogen transport and survival is possible if these types of wastes are disposed as
MSW. However, there is little experimental data available for the determination of patho-
gens in leachates or in runoff from a landill. Approximately 15% of hospital waste is
infectious. Medical waste incinerators are used by 70% of U.S. hospitals. There is little
regulation of these incinerators due to their small size. As a result in some states, between
48% and 87% of the incinerators have no emission control equipment (Washington State
Department of Ecology, 1989). Low level radioactive waste is generated through various
medical procedures involving radiopharmaceuticals, radiology, and nuclear medicines.
However, this type of waste from hospitals is less than 5% of the total waste in the United
States (U.S. Congress OTA, 1989). Most of these wastes have a very short half-life and can
be stored on site.
Between 220 and 380 m
3
of water are required per tonne of paper produced (Badar and
Farooqi, 2012). Efluent solids, biological oxygen demand, color, and toxicity are present in
the wastewater. Approximately 30% to 70% of the contaminants are removed during treat-
ment. The pulping and bleaching stages are the major sources of contaminants. Sludge
generation is in the range of 14 to 140 kg/tonne of pulp. The generation of dry sludge is
approximately 4.3% of the final paper product and in the case of recycled paper mills,
increases to 20%-40% (World Bank, 2007).
In the United States, total sludge generation is about 2.5 million tonnes/year. Chlorinated
organic compounds can be released from the sludge. Chlorine and compounds of chlo-
rine are used in the bleaching of wood pulp particularly by the kraft or sulite processes.
Proesses using elemental chlorine produce signiicant quantities of dioxins. However, by
replacing elemental chlorine with chlorinedioxide, this procedure has reduced dioxin pro-
duction substantially, and since 1990 elemental chlorine free (ECF) and totally chlorine
free (TCF) processes have replaced element chlorine bleaching. Although these levels have
been reduced, the pH of the sludge is typically still higher than 12.5.
Energy consumption trends have shifted in recent years. From 1972 to 1999, wood wastes,
spent liquor solids and other internal sources of energy have increased from 41% of the
energy used to 58%, thus relying less on fossil fuels. The U.S. Environmental Protection
Agency has found that paper recycling instead of production of virgin paper has reduced
water contamination by 35% and air contamination by 74% (USEPA, 2007).
In 1991, according to the U.S. Bureau of Mines, more than 1.15 billion tonnes of concrete
were produced worldwide. According to the Strategic Development Council (2002), this
amount has increased to more than 6 billion tonnes. Cement is the main ingredient of con-
crete. A typical mix is 12% Portland cement, 34% sand, 48% crushed stone and 6% water, all
of which are abundant. However, transportation can be a main issue, and water require-
ments for washing and reduction of the impact of dust. Fly ash, a waste from coal-ired
power plants, is now present at a proportion of about 9% in cement. Energy consumption
is considerable in cement production. Addition of ly ash with concrete can make the pro-
cess more energy eficient. Since coal is often used for energy emissions of carbon dioxide,
sulfur, and nitrous oxide are high, carbon dioxide emissions are estimated at 1200 kg CO
2
/
tonne of cement, 60% from energy use and the other 40% from calcining. Dust emissions
are also signiicant (180 kg/tonne of cement produced) but should be controlled as much
as possible by water sprays, hoods, etc. Other contaminants include sulfur dioxide and
nitrous oxide from both fuels and raw materials. Water contamination from washwater of
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