Secondary wastewater treatment

Ammonium Ion Removal. A fixed-bed molecular-sieve ion-exchange process has been commercialized for the removal of ammonium ions from secondary wastewater treatment effluents. This application takes advantage of the superior selectivity of molecular-sieve ion exchangers for ammonium ions. The first plants employed clinoptilolite as a potentially low cost material because of its availability in natural deposits. The bed is regenerated with a lime-salt solution that can be reused after the ammonia is removed by pH adjustment and air stripping. The ammonia is subsequentiy removed from the air stream by acid scmbbing. 

In secondary wastewater treatment plants receiving silver thiosulfate complexes, microorganisms convert this complex predominately to silver sulfide and some metallic silver (see Wastes, INDUSTRIAL). These silver species are substantially removed from the treatment plant effluent at the settling step (47,48). Any silver entering municipal secondary treatment plants tends to bind quickly to sulfide ions present in the system and precipitate into the treatment plant sludge (49). Thus, silver discharged to secondary wastewater treatment plants or into natural waters is not present as the free silver ion but rather as a complexed or insoluble species. 

The Willamette River Basin, Oregon serves as an excellent case study of river quality assessment for a number of reasons. First, the Willamette River has been cited internationally as a classic example of how water quality can be restored from a previously poor quality waterway (1-3). Second, excellent background data were available, particularly on hydrology. Third, at the time most of these studies were initiated, the Willamette River was the largest river in the U.S. for which all point-source discharges were receiving secondary wastewater treatment. 

Due to the large volumes of water used in pulp and paper processes, virtually all U.S. mills have primary and secondary wastewater treatment systems to remove particulates and BOD. These systems also provide significant removals (e.g., 30 to 70%) of other important parameters such as AOX and chemical oxygen demand (COD). 

Secondary wastewater treatment, 25 888 Second falling rate period, 23 66 Second-generation ionic liquids, 26 838, 847, 865... 

Wastewater is treated in on-site wastewater treatment facilities and then discharged to publicly owned treatment works (POTWs) or discharged to surface waters under National Pollution Discharge Elimination System (NPDES) permits. Petroleum refineries typically utilize primary and secondary wastewater treatment. 

Primary biosolids (settleable and suspended solids) are present at a level of a few percent in the influent wastewater and are produced at a rate of about 0.091 dry kg/person-day (0.20 dry Ib/person-day). Per million population, this corresponds to the production of 33,200 t/year of primary biosolids. After conventional primary and secondary wastewater treatment, the digested, dewatered biosolids are reduced to the equivalent of about 0.063 dry kg/person-day (0.14 dry Ib/person-day), or 23,000 dry t/year per million population. For the United States in 1995, primary and treated biosolids production were about 8.6 and 5.9 million dry tonnes. 

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. 

POTW EXPERT address three types of secondary wastewater treatment processes suspended growth, fixed film, and stabilization ponds. The expert system emphasizes meeting National Pollutant Discharge Elimination Standards (NPDES) for secondary treatment facilities (30 mg/1 B0D5 and TSS) with a maximum average daily flow of 20 million gallons per day (mgd). 

The POTW EXPERT system demonstrates that a microcomputer-based expert system can effectively represent a complex evaluation methodology, evaluate the capability of a secondary wastewater treatment facility s major unit processes, detect factors which potentially limit performance, and categorize them according to their influence on plant performance. The model is presented in a logical and structured manner to allow wastewater professionals unfamiliar with the CPE process to effectively employ this wastewater treatment methodology. 

U.S. conditions of primary and secondary wastewater treatment plants averaged monthly over 20 U.S. cities. 

Figure 8. Trickling filter for secondary wastewater treatment (Manahan, 1994).

Even a combination of primary and secondary wastewater treatment systems will not remove dissolved inoi anic materials such as toxic metal ions, nutrients such as nitrate ions (NO ) or ammonium ions (NH ), or non-biodegradable organic compounds such as chlorinated hydrocarbons. These materials can be removed by a variety of tertiary wastewater treatment methods that are selectively introduced where the nature of the wastewater requires them. One obstacle to tertiary treatment is the initial expense of modifying sewage treatment plants and the ongoing expense of additional treatment. 

Secondary wastewater treatment operates under (aerobic/anaerobic) conditions. 

Lin, H., Chen, J., Wang, F., Ding, L., Hong, H. (2011). Peasibriity evaluation of submerged anaerobic membrane bioreactor for municipal secondary wastewater treatment. Desalination, 280, 120—126. 

The effluent from secondary wastewater treatment generally contains 300-400 mg/L more dissolved inorganic material than does the municipal water supply. Therefore, complete water recycling requires inorganic solute removal. Even when water is not destined for immediate reuse, the... 

Low solid content feedstocks (eg, secondary wastewater treatment, wastewater from food industry, hydraulic flush manure systems) ... 

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