Wastewater treatments

However, wastewater usually contains ammonium instead of nitrate, which should be previously oxidized. Ammonium oxidation to nitrate could be done in situ in a BES or in an external compartment. This concept was demonstrated by coupling a double-chamber MFC with a nitrifying bioreactor [131, 153] or by introducing a low dissolved oxygen concentration in the cathode [154,155]. 

An MEC has also been applied to treat domestic and industrial (winery and swine) wastewaters. Swine wastewater with a COD of 12-17 gl was treated with COD removal efficiencies ranging from 19 15 to 72 4%, with hydrogen recoveries of 17 7 to 28 d= 6% based on COD removal [147]. Organic matter removal efficiency and energy recovery were higher for MFC- than MEC-treated winery and domestic wastewaters. The energy recovery for winery wastewater in MFCs was 0.26 kWh kg COD compared with —0.32 kWh kg COD for MFCs. Hydrogen production costs of winery and domestic wastewaters with as MEC were determined as 4.51 kg H2 for winery wastewater and 3.01 kg H2 for 

Cell type Application Volume (ml) Operational mode Current (power) density Output Ref. 

2 Caustic soda production 3313 Lamellar-type reactor -1.77 V NaOH (3.4wt%) [150] 

Most of the wastewater from German pulp and paper mills is treated biologically, either in municipal treatment plants (18% of production volume) or in in-mill plants (74% of production volume). 4% of the annual paper volume is produced in mills with a totally closed water circuit which means that these mills are absolutely effluent free [2]. 

Fats present in wastewater are nondegradable, causing the generation of nnpleasant odors, foam formation, and solidification at low temperatures (Rigo et al., 2008). Lipases have potential applications in wastewater treatment, as they reduce fat and minimize byproduct formation by using mild conditions, and reducing energy needs and costs. 

7 EQUIPMENT SIZING AND CAPITAL COST ESTIMATION USING THE ASPEN ICARUS PROCESS EVALUATOR (IPE) 

This section is provided in the file Section 16.7.pdf on the CD-ROM that accompanies this book. It introduces Aspen IPE and shows how to estimate equipment sizes, purchase costs, installation costs, and the total permanent investment. Two examples are provided  

Depropanizer distillation tower. This tower is presented on the CD-ROM (either 

HYSYS Separations — Distillation or ASPEN PLUS Separations — Distillation. Ref- 

Monochlorobenzene separation process. This process was introduced in Section 4.4, with simulation results using ASPEN PLUS provided on the CD-ROM (ASPEN PLUS — Principles of Flowsheet Simulation Interpretation of Input and Output — Sample Problem). Beginning with the file, MCB.bkp, the equipment sizes, purchase costs, and installation costs are estimated using Aspen IPE. 

The mechanical effects of cavitational collapse together with the production of radical species combine to provide the essential elements for water 

Ultrasound is particularly effective in surface decontamination where the cleaning action induced by cavitational collapse near a surface will 

2 Chemical decontamination. One of the major goals in waste-water treatment is the removal or destruction of chemical pollutants. Such materials may be of agricultural origin (e.g. pesticides) or from industry (e.g. effluent from chemical factories or stormwater run-off). Much effort has been devoted to this area using conventional technology and newer systems involving electro- and photochemistry. Over the past few years there has been extensive research into this field. 

The use of ultrasound for the destruction of dilute aqueous solutions of low molecular weight organic compounds (alcohols, ketones and aldehydes) at ambient temperature has been reported. An aqueous flow cell system was assembled to measure the oxidatively degraded formate and acetate products by on-line ion chromatography [48]. 

The degradation of a number of 2-, 3- and 4-chlorophenol, have been examined under pulsed sonolytic conditions (20 kHz, power, 50 W cm ) in air-equilibrated aqueous media [52]. These phenols are totally transformed to dechlorinated, hydroxylated intermediate products via first-order kinetics in a time of between 10 and 15 h. The process involves hydroxyl radical attack and at low concentrations of chloro-phenol the reaction takes place in the bulk solution whereas at the higher concentrations the reaction occurs predominantly at the gas bubble/liquid interface. 

Several characteristics are used to describe sewage. These include turbidity (international turbidity units), suspended solids (ppm), total dissolved solids (ppm), acidity (H ion concentration or pH), and dissolved oxygen (in ppm Oj). Biochemical oxygen demand (BOD) is used as a measure of oxygen-demanding substances. 

Waste from a municipal water system is normally treated in a publicly owned treatment works (POTW). In the United States, these systems are allowed to discharge only effluents that have attained a certain level of treatment, as mandated by federal law. One of the major objectives in the treatment of hazardous wastes, which usually have a high content of water, is to bring the water byproduct up to a quality that can be sent to a POTW for treatment and release. 

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Wastewater treatment processes are generally classified in order as... 

TABLE 11.2 Comparison of Aerobic and Anaerobic Wastewater Treatments... 

Table 11.2 provides a summary of the main features of aerobic and anaerobic wastewater treatment. Aerobic treatment processes are generally restricted to BOD < 1000 mg/liter unless pure oxygen is used for aeration. 

Schroeder, E. D., Water and Wastewater Treatment, McGraw-Hill, New York, 1977. 

Figure 10.15 shows a simplified diagram for effluent gas and wastewater treatment. 

Samples from municipal wastewater treatment plants and samples of industrial discharges often are collected as 24-h composites. Samples are obtained using an automatic sampler that periodically removes individual grab samples. The volume of each sample increment and the frequency of sampling may be constant or may vary in response to changes in flow rate. 

Another important example of redox titrimetry that finds applications in both public health and environmental analyses is the determination of dissolved oxygen. In natural waters the level of dissolved O2 is important for two reasons it is the most readily available oxidant for the biological oxidation of inorganic and organic pollutants and it is necessary for the support of aquatic life. In wastewater treatment plants, the control of dissolved O2 is essential for the aerobic oxidation of waste materials. If the level of dissolved O2 falls below a critical value, aerobic bacteria are replaced by anaerobic bacteria, and the oxidation of organic waste produces undesirable gases such as CH4 and H2S. 

The urea produced is normally either prilled or granulated. In some countries there is a market for Hquid urea—ammonium nitrate solutions (32% N). In this case, a partial-recycle stripping process is the best and cheapest system. The unconverted NH coming from the stripped urea solution and the reactor off-gas is neutralized with nitric acid. The ammonium nitrate solution formed and the urea solution from the stripper bottom are mixed, resulting in a 32—35 wt % solution. This system drastically reduces investment costs as evaporation, finishing (priQ or granulation), and wastewater treatment are not required. 

Under the pressure of progressively more stringent government regulations with regard to permissible levels of residual NH and urea content in wastewaters, the fertilizer industry made an effort to improve wastewater treatment (see also Water, sewage). 

All process Hcensors also feature wastewater treatment systems. Stamicarbon guarantees the lowest NH —urea content and has plants in operation confirming the low NH —urea (1 ppm NH —1 ppm urea). This water is very satisfactory to use as boiler feed water. See Figures 16 and 17 for this system. 

The function of aeration in a wastewater treatment system is to maintain an aerobic condition. Water, upon exposure to air, tends to estabUsh an equihbrium concentration of dissolved oxygen (DO). Oxygen absorption is controlled by gas solubiUty and diffusion at the gas—hquid interface. Mechanical or artificial aeration may be utilised to speed up this process. Agitating the water, creating drops or a thin layer, or bubbling air through water speeds up absorption because each increases the surface area at the interface. 

Dissolved matter lowers oxygen solubihty. At 20°C and 101.3 kPa (1 atm), the equihbrium concentration of dissolved oxygen in seawater is 7.42 mg/L. It is 9.09 mg/L in chloride-free water and 9.17 mg/L in clean water. This lessening of oxygen solubihty is of importance to wastewater treatment. The solubihty of atmospheric oxygen in a domestic sewage is much less than in distilled water (12). 

N. A. Shapka, ed.. Wastewater Treatment in the Militay Explosives and Propellant Production Industy, Report NC-02T, 3 Vols., ADPA, Washington, D.C., 1975. 

The production building is only one part of a full-fledged fine chemicals plant. Apart from the multipurpose plant building there is usually an office and R D building, the warehouse, the maintenance shop, tank farms, the iaciaerator, and wastewater treatment faciUties. 

In the area of municipal and iadustrial wastewater treatment, the principal environmental issue is the toxicity of residual flocculating agents ia the effluent. Laboratory studies have shown that cationic polymers are toxic to fish because of the iateraction of these polymers with giU. membranes. Nonionic and anionic polymers show no toxicity (82,83). Other studies have shown that ia natural systems the suspended inorganic matter and humic substances substantially reduce the toxicity of added cationic polymer, and the polymers have been used successfully ia fish hatcheries (84—86). Based on these results, the EPA has added a protocol for testing these polymers for toxicity toward fish ia the presence of humic acids (87). The addition of anionic polymers to effluent streams containing cationic polymers to reduce their toxicity has been mentioned ia the patent Hterature (83). 

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