Wastewater minimization operating

In the presence of wastewater minimization, the sequence constraints initially presented in Chapter 2 are modified as follows. The following constraints stipulates that the task corresponding to state s n. can only commence once all the previous tasks and their corresponding washing operations are complete. 

Apart from biocatalyst activity, several other parameters are important in development of a biodesulfurization process. These parameters include oil/water ratio, composition of aqueous phase used for biocatalyst suspension during desulfurization, biocatalyst loading, oil/water separation following completion of desulfurization, potential for biocatalyst recycle, recycle of aqueous phase to reduce fresh water usage and wastewater minimization, as well as secondary oil separation and purification operations. 

Wastewater treatment systems can be classified, in addition to pretreatment, as preliminary, primary, secondary, and tertiary (advanced) treatments. Pretreatment of industrial wastewater is required to prevent adverse effects on the municipal wastewater treatment plants. Preliminary treatment is considered as any physical or chemical process that precedes primary treatment. The preliminary treatment processes may consist of influent screening and grit removal. Its function is mainly to protect subsequent treatment units and to minimize operational problems. Primary treatment is defined as the physical or chemical treatment for the removal of settleable and floatable materials. The screened, degritted raw wastewater from preliminary treatment flows to the primary clarification tanks, which are part of the primary treatment facilities. Secondary wastewater treatment is the process that uses biological and chemical treatment to accomplish substantial removal of dissolved organics and colloidal materials. The secondary treatment facilities may be comprised of biological reactor and secondary clarification basins. Tertiary (advanced) wastewater treatment is used to achieve pollutant reductions by methods other than those used in primary and secondary treatments. The objective of tertiary wastewater treatment is to improve the overall removal of suspended solids, organic matter, dissolved solids, toxic substances, and nutrients. 

Pulp bleaching with chlorine dioxide is most often performed at an acidic pH, so that the final pH of the bleach Hquor is in the range of 2—5. Under these conditions, the residual concentration of chlorite and chlorate ions in the bleach Hquor are minimized and chloride ion is the predominant chlorine species in the spent bleach (77). In addition to direct addition to pulp in bleaching, chlorine dioxide also finds use in wastewater treatment from pulp mill operations as a means to remove effluent color (85). 

So far the discussion on water minimization has restricted consideration to identify opportunities for water reuse. Maximizing water reuse minimizes both fresh water consumption and wastewater generation. However, the process constraints for inlet concentrations, outlet concentrations and flowrates have so far been fixed. Often there is freedom to change the conditions within the operation. Typical process changes that might be contemplated include ... 

Consider the data in Table 26.10 for three water-using operations. It is desired to minimize the consumption of freshwater and generation of wastewater. A regeneration process is available with a performance that can achieve an outlet concentration of 5 ppm. 

Auxiliary processes. Refineries also have other processes and units that are vital to operations by providing power, waste treatment, and other utility services, such as boilers, wastewater treatment, and cooling towers. Products from these facilities are usually recycled and used in other processes within the refinery and are also important with regard to minimizing water and air pollution. 

During recent years there has been an increasing demand for better operation of wastewater treatment plants in order to guarantee satisfactory effluent quality at minimal cost. The renewed interest in instrumentation and control comes after a period of huge investments in sewer networks and treatment plants. Several factors have contributed to the potential for better operation and control, such as cheap computing power, improving sensors and better knowledge of process dynamics and control. 

Labor costs should be minimized, as with any manufacturing operation. Depending upon the robustness of the system and the amount of process control instrumentation, it might in later generations of the system be possible to achieve unattended or remote operation of a biological H2 production facility. Using a wastewater treat-... 

The comparison of the AOPs technologies is often made only in terms of efficiency in the removal of pollutants, but a more correct analysis should takes into account several parameters (i) safety of operations, (ii) manageability and applicability to the specific operations (for example, when small volume effluents dispersed over a wide territory, it may be preferable to transport the water treatment unit instead rather than to collect all wastewater in a single central treatment unit), (iii) technical effectiveness using real streams, (iv) absence of necessity of post-treatments (to eliminate some residual compounds, even in traces, or metal ions), (v) secondary pollution prevention, (vi) minimal toxicity of... 

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