Effluent, quality

A comprehensive analytical program for characterising wastewaters should be based on relevance to unit treatment process operations, the poUutant or pollutants to be removed ia each, and effluent quality constraints. The qualitative and quantitative characteristics of waste streams to be treated not only serve as a basis for sising system processes within the facility, but also iadicate streams having refractory constituents, potential toxicants, or biostats. Such streams are not amenable to effective biological treatment, as iadicated by the characterization results, and requite treatment usiag alternative processes. 

Processes for SS separation may fill three distinct functions in wastewater treatment, namely, pretreatment to protect subsequent processes and reduce their loadings to required levels, treatment to reduce effluent concentrations to required standards, and separation of solids to produce concentrated recycle streams required to maintain other processes. In the first two functions effluent quality is the prime consideration, but where the third function must be fulfilled along with one of the others, design attention must be given to conditions for both the separated solids (sludge) and the process effluent. 

The proper measure of flocculation effectiveness is the performance of subsequent solids separation units in terms of both effluent quality and operating requirements, such as filter backwash frequency. Effluent quality depends greatly on the reduction of residual primary size particles during flocculation, while operating requirements relate more to the floe volume applied to separation units. 

Ultrafiltration equipment are combined with other unit operations. The unique combination of unit operations depends on the wastewater characteristics and desired effluent quality, and cost considerations. 

In mixed-bed units, both the cation and the anion resins are mixed together thoroughly in the same vessel by compressed air. The cation and the anion resins being next to each other constitute an infinite number of cation and anion exchangers. The effluent quality obtainable from a well-designed and operated mixed-bed exchanger will readily produce demineralized water of conductivity less than 0.5 mmho and silica less than 10 ppb. 

Clearly, this problem is serious because the minimum polisher effluent quality is determined by the maximum impurity concentration in reactor water, and current industry guidelines limit chloride and sulfate to below 5 ppb in reactor water. 

Comparison of Effluent Quality before and after Process Modification... 

Alternatively, hexavalent chromium can be reduced, precipitated, and floated by ferrous sulfide. By applying ferrous sulfide as a flotation aid to a plating waste with an initial hexavalent chromium concentration of 130 mg/L and total chromium concentration of 155 mg/L, an effluent quality of less than 0.05 mg/L of either chromium species can be achieved if a flotation-filtration wastewater treatment system is used.15... 

Table 6.3 shows the characteristics of a typical effluent discharge from a conventional reduction-precipitation system. The effluent quality meets industrial pretreatment requirements. 

The advantage of ex situ biological treatment is the ability to control the effluent quality. The use of air for aerobic treatment is easier to control and costs less. Nutrient can be added more effectively and the temperature can be controlled. 

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). 

Table 26.3 Typical effluent quality for various receiving waters7.

The residence time of the wastewater in a sewer may, under dry-weather conditions, be of the same order of magnitude as that found in treatment plants. In-sewer chemical and microbiological processes are, therefore, of specific interest under such conditions. This volume shows in detail that the microbiological transformations of wastewater in sewers relate directly to the treatment processes and, thereby, to the changes in effluent quality. 

Each type of technique can be applied in several modifications. Microbiological degradation processes offer the possibility to purify wastewater streams which contain a wide range of organic pollutants. In contrast, physical/chemical techniques are much more specific. The quality of the purified water regarding residual amounts of soluble organic pollutants, and colloidal and suspended particle pollutants, strongly depends on the type of treatment process and the applied treatment conditions. Very often a combination of different types of treatment techniques is necessary to satisfy the effluent quality required (for example a combination of anaerobic and aerobic treatment). 

Some forms of nutrient pollution may be found under conditions where deoxygenation is not a serious problem, and this has often been observed at the site of paper mill discharges. These forms of pollution manifest themselves as a voluminous growth of filamentous bacteria and they sometimes occur as effluent quality is improving. 

Improvements have been identified and demonstrated that may afford a lower corrosion rate for SCWO liners and improve effluent quality for all chemical agents, including GB (see the two rightmost liner configurations in Figure 5-2). 

A biological step is always necessary to remove the carbonaceous fraction from the influent wastewater suspended biomass treatments are the most common. These entail long SRTs (>25-30 d), and compartmentalization of the biological reactor is necessary for the removal of recalcitrant compounds. Furthermore, as many micro-pollutants tend to adsorb/absorb to the biomass flocks, efficient solid/ liquid separation can greatly improve their removal from wastewater and, at the same time, guarantee consistently good effluent quality. MBRs have been suggested for this purpose by many authors [9, 58, 80, 93], some of whom found that ultrafiltration (UF) membranes are more efficient than MF membranes [9, 93]. 

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