Tertiary Treatment Processes

Tertiary treatment or polishing treatment prepares the aqueous waste for final discharge. The final quality of the effluent depends on the nature and flow of the receiving water. Table 26.3 gives an indication of the final quality required7. 

Stable end products (C02, Unstable end products Stable and unstable end 

BOD5 removal up to 95% BOD5 removal 75-85% BOD5 removal 60-80% 

High sludge formation Low sludge formation No sludge disposal or centrifugation 

Gravity separation Centrifugal separation Filtration Membrane filtration Coalescence Centrifugal separation Flotation Wet oxidation Thermal oxidation Biological oxidation (aerobic, anaerobic, reed beds) Chemical oxidation Activated carbon Wet oxidation Thermal oxidation 

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There are four stages preliminary, primary, secondary, and tertiary treatment processes, which differ mainly by the number of operations performed on the waste steams (2,3). 

Distributed effluent treatment requires that a philosophy of design be adopted that segregates effluent for treatment wherever appropriate, and combines it for treatment where appropriate. Various primary, secondary and tertiary treatment processes are available to achieve the required discharge concentrations. 

Tertiary treatment processes are used only to eliminate materials which are not amenable to secondary treatment. A treatment method for wool scouring effluent has been developed, consisting of evaporation and incineration plant in combination with a biological plant [56]. The resulting condensates from the evaporation plant and the incineration residues are recycled so that the water, ammonia and scouring aids are returned to the production plant [57]. 

Tertiary treatment processes remove specific pollutants, including traces of benzene and other partially soluble hydrocarbons. Tertiary water treatment can include ion exchange, chlorination, ozonation, reverse osmosis, or adsorption onto activated carbon. Compressed oxygen may be used to enhance oxidation. Spraying the water into the air or bubbling air through the water removes remaining traces of volatile chemicals such as phenol and ammonia. 

Tchobanoglous, George, Jeannie Darby, Keith Bourgeons, John McArdle, Paul Genest, and Michael Tylla, Ultrafiltration as an Advanced Tertiary Treatment Process for Municipal Wastewater, Desalination, 119, 315-322 (1998). 

The main tertiary treatment process is then a filtration one, using either a sand bed or a membrane process, usually microfiltration, possibly followed by ultrafiltration. There may also be too high a content of nitrogen and phosphorus, and this will require additional biological processes, with some more sludge to be separated. 

Process water streams from vinyl chloride manufacture are typically steam-stripped to remove volatile organics, neutralized, and then treated in an activated sludge system to remove any nonvolatile organics. If fluidized-bed oxychlorination is used, the process wastewater may also contain suspended catalyst fines and dissolved metals. The former can easily be removed by sedimentation, and the latter by precipitation. Depending on the specific catalyst formulation and outfall limitations, tertiary treatment may be needed to reduce dissolved metals to acceptable levels. 

Continued recycling of effluent would soon give an unusable product, and tertiary treatment, although expensive, is essential. In some instances, considerable amounts of water can be saved by careful housekeeping and process change. 

Fluidized-bed powdered activated carbon systems represent another important process. The use of activated carbon for the tertiary treatment of secondary sewage effluents has been used extensively. Powdered carbon is as effective as granular activated carbon for removing the organic impurities from the wastewater. 

Before powdered carbon can be used commercially or reused for tertiary treatment of sewage effluents, a method of regeneration is required. The use of the fluidized bed for regeneration offers the key advantages of excellent temperature and atmosphere control and the ability to process the powdered solids conveniently and continuously. 

Where effluents require primary, secondary and possibly additional tertiary treatment, attention should be paid to the various treatment processes with regard to personnel safety and public sensitivity to on-site treatment. 

To meet the specified standard,4 wastewaters are often subjected to a series of treatment processes before they are discharged into the environment, particularly, water bodies. The treatment processes include physical, chemical, and biological processes that may be applied singly or collectively. The collective application of the processes can be employed in a variety of systems classified as primary, secondary, and tertiary wastewater treatment, to achieve different levels of contaminants removal.2... 

Vourch et al49 studied the applicability of the RO process for the dairy industry wastewater. The treated wastewater total organic carbon (TOC) was <7 mg/L. It was found that in order to treat a flow of 100 m3/d, 540 m2 of the RO unit is required with 95% water recovery. Dead-end NF and RO were studied for the treatment of dairy wastewater.50 Permeate COD, monovalent ion rejection, and multivalent ion rejection for the dead-end NF were reported as 173-1095 mg/L, 50-84%, and 92.4-99.9%, respectively. When it comes to the dead-end RO membranes, the values for permeate COD, monovalent ion removal, and multivalent ion removal were 45-120 mg/L, >93.8%, and 99.6%, respectively. Membrane filtration technology can be better utilized as a tertiary treatment technology and the resultant effluent quality will be high. There can be situations where the treated effluents can be reused (especially if RO is used for the treatment). 

Chemical treatment is what the name implies-the addition of a foreign substance to effect the removal of unwanted substances. This includes such operations as neutralization, coagulation, ion exchange, and electrodialysis. These, along with the advanced physical systems, have been referred to at times as tertiary treatment or advanced treatment processes. 

Advanced wastewater treatment techniques, for example oxidation processes, can achieve up to 100% removal for diclofenac [52,53], Reverse osmosis, activated carbon and ozonation have been shown to significantly reduce or eliminate antibiotics from wastewater effluents [32], The efficiency of two tertiary treatments, chlorination and UV disinfection, was compared and chlorination led to lower quantities of antibiotics [54],... 

Many municipalities also require tertiary treatment. There are a number of tertiary processes, most involving filtration of some sort. A common method is to pass secondary effluent through a bed of finely powdered carbon, which captures any remaining particulate matter and many of the organic molecules not removed in earlier stages. The advantage of tertiary treatment is greater protection of our water resources. Unfortunately, tertiary treatment is cosdy and ordinarily used only in situations where the need is deemed vital. 

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