Waste Water Treatment Plant

General Waste Water Treatment Plant at  Coal Fired Power Plant

Waste Water Treatment Plant must be there in every coal fired power plant. The reasons are the following : 

1. to prevent marine life
2. a matter of caring for our environment and for our own health
3. prevent sea shore
4. protection of public life
5. reuse the treated effluent, for agriculture, for groundwater recharge, for industrial recycle
6. solving social problem caused by the accumulation of wastewater

If wastewater is not properly treated, then the environment and human health can be negatively impacted.

The general waste water treatment chart is below:

figure 1. waste water treatment chart

The explanation of the above chart :

At least two sources or input in Waste Water Treatment : Water Treatment Plant Neutralization Basin, blow down of Boiler. Waste source goes to Retention Basin. The main process in the Waste Water Treatment are pH Adjustment, Coagulation and Flocculation. NaOH is injected to adjust pH around 6 - 8. Coagulation is destabilization process of suspended solid or colloid material  with coagulation sunstance (FeCl3) to produce micro floc using rapid mixing. After that, the process is going to flocculation by Polymer. Flocculation is the floc formation process which basically uses agglomeration grouping between particles and coagulats with gentle mixing to combine several particles into large floc.

In Clarifier, sedimentation is happen in bottom and clear water (supernatant) in the above. Solid which formed by sedimentation is treated in Sludge Dewatering Unit. Clear water is going to Neurtalization Tank to adjust pH ( 6 - 8 ) before discharging to sea or outfall. The parameters of treated water must be monitoring are: 

pH                                                                                       6.5 - 8.5

TSS (total suspended solid)                                               30 mg/l

COD (chemical oxygen demand)                                       100 mg/l

BOD (biological oxygen demand)                                       20 mg/l

The definition of above parameters:

1. pH: This is a method of expressing the acid condition of the wastewater. pH is expressed on a scale of 1 to 14. For proper treatment, wastewater pH should normally be in the range of 6.5 to 9.0.  The determination of pH value of sewage is important, because of the fact that efficiency of certain treatment methods depends upon the availability of a suitable pH value.
2. Total Suspended Solids (TSS) refers to any particles that are suspended in the water column. These particles can include silt, algae, sediment, and other solids floating in the water (both organic and inorganic). These particles are defined as being large enough to not pass through the filter (through the filtration process) used to separate them from the water. Suspended solids absorb heat from sunlight and as a result, the water temperature increases resulting in a deprivation of dissolved oxygen in the water which can be disastrous to aquatic life if levels are too high. TSS can be measured in ppm, mg/L, g/L and %.
3. Chemical oxygen demand (COD) is the amount of chemical oxidation required to convert organic or anorganic matter in water and wastewater to carbon dioxide. The chemical oxygen demand (COD) of a raw water or a wastewater is determined by performing a laboratory test on the given wastewater with a strong oxidant like dichromate solution; and the theoretical computations of COD are only performed on water solutions prepared with the known amounts of specific organic compounds in laboratory situations to compare the theoretical and test results, and to establish the limitations of the test procedures.The high COD means need much oxygen to oxidize so less oxygen that can be used by organism or fish. As a result, the organism or fish tend to die.
4. Biochemical oxygen demand (BOD) is used as a measure of the quantity of oxygen required for oxidation of biodegradable organic matter present in the wastewater by aerobic biochemical action. The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °. The rate of oxygen consumption in a wastewater is affected by a number of variables: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the wastewater. BOD directly affects the amount of DO within the wastewater. Normally the BOD must be less than COD.