Oil & Grease:
Animal fat, vegetable and petroleum oils are not quickly broken down by bacteria and can cause permanent pollution in receiving environments. When large amounts of oils and greases are discharged to receiving waters from community systems, they may float to the surface and harden, causing aesthetically unpleasing conditions. The floating oils and grease decreases the oxygen transfer efficiency of water causing septic condition.
They also can bind with solid proteins, carbohydrate and other materials, causing foul odors, attracting flies, mosquitoes and other disease vectors.
Solids:
Solid materials in wastewater can consist of organic and/or inorganic materials. The solids must be significantly reduced by treatment or they would increase BOD when discharged to receiving waters and provide places for microorganisms to escape disinfection. They can also clog soil absorption fields in onsite systems.
Settleable solids - certain substances, such as sand, grit, and heavier organic and inorganic materials settle out from the rest of the wastewater stream during the preliminary stages of treatment. On the bottom of settling tanks and ponds, organic material makes up a biologically active layer of sludge that aids in treatment.
Suspended solids - materials that resist settling may remain suspended in wastewater. Suspended solids in wastewater must be treated, or they will clog soil absorption systems and reduce the effectiveness of disinfection systems.
Dissolved solids - small particles of certain wastewater materials can dissolve like salt in water. Microorganisms in wastewater consume some dissolved materials, but others, such as heavy metals, are difficult to remove by conventional treatment. Excessive amounts of dissolved solids in wastewater can have adverse effects on the environment.
Heavy metals:
Do you suspect heavy metals to be present in sewage? Municipal wastewater also contains a variety of potentially toxic elements such as arsenic, cadmium, chromium, copper, lead, mercury, zinc, etc. Even if toxic materials are not present in concentrations likely to affect humans, they might well be at phytotoxic levels, which would limit their agricultural use. However, from the health point of view, the greatest concern in the agricultural use of wastewater are the pathogenic micro and macro organisms.
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