Environmental Engineering Reference
In-Depth Information
emissions are nitrogen oxides, volatile organic compounds, bioaerosols, and odor compounds
such as ammonia, mercaptans, and hydrogen sulfide (El-Fadel and Massoud, 2001).
Advanced water treatment
Conventional water treatment plants have three defined processes: pretreatment, primary
treatment, and secondary treatment. In addition, wastewater plants can be equipped with a
tertiary treatment level generally known as “advanced water treatment.”
Wastewater treatment plants equipped with advanced water treatment systems further pol-
ish wastewater treated with regular activated sludge plants to remove chemical compounds
and microorganisms that produce ecotoxicity. Some of the technologies used in advanced
water treatment are sand filtration, membrane bioreactors, membrane filtration, ozone treat-
ment, and ultraviolet treatment, which can be applied individually or in combination. Pollutants
targeted are endocrine disruptors, heavy metals, nutrients, and detergents. From the technical
point of view, advanced water treatment can achieve the goals of removing the offending
compounds in most cases; however, this further treatment comes at the price of additional
expenditures of electricity with the resulting indirect emissions of GHGs. For instance, water
treatment with reverse osmosis takes between 9 and 17 kWh/1,000 gallons (Russell, 2006).
The use of advanced water treatment makes water clean enough for reclamation and reuse.
Examples of reclaimed water applications are landscape irrigation, fire protection systems,
toilet flushing, environmental reuse in wetlands and groundwater replenishment, cooling tow-
ers, and boilers. The use of reclaimed water is generally regulated, so local, state, and federal
regulations need consultation before starting any project on reuse of reclaimed water.
Minimizing solids in wastewater
Conventional methods
In aerobic systems, fewer solids in wastewaters translate into less energy to treat the effluent;
therefore, the impact of wastewater treatment is reduced by controlling the solid content of the
wastewater.
At the processing plant, solids need to be managed dry as much as possible to prevent
leaching into wastewater streams. If contact is unavoidable, then the minimization of the
contact time will decrease leaching.
The most effective way to prevent leaching of compounds (i.e., proteins, carbohydrates,
and fats) into water streams is capture at the source. The use of vibrating screens is an effective
method to separate solids from water streams right at point of production. Depending on the
volume, solids can be accumulated in bins or totes and transported periodically for small vol-
umes or retrieved and transported continually with a conveyor belt or a pneumatic system for
larger volumes.
In steps of the process where solid waste is generated constantly (e.g., in trimming tables),
permanent conveyor belts are the best alternative to transport the waste directly to outside
containers. Personnel needs proper training on the importance of correct handling of solid
waste and instructed not to throw trims and waste to the floor that eventually would be washed
down the drain.
Even with an effective source separation system in place, some solids always end up in
wastewater stream; therefore, other procedures need to be used to remove solids before send-
ing the wastewater for treatment. Conventional technologies to separate solids and nonmisci-
ble liquids from water streams include flotation, centrifugation, evaporation, filtration, and
sedimentation.
