Secondary treatment wastewaters, reuse

As the MBR process does not need the secondary clarifier for the solid-liquid separation, it can prevent these inherited problems that occur in the conventional processes for the wastewater reclamation (29). The resulting high-quality and completely disinfected effluent means that the MBR process can be used for many purposes, i.e., industrial and municipal wastewater treatment and reuse (30). More important, the land requirement of MBR is much less than that of conventional wastewater reclamation processes. 

With world population increase and scarcity of water sources, the key to providing a sustainable development of water resources is to carry out water reclamation. The concept of water reclamation is to treat wastewater from different sources to meet different water quality requirements of various water applications economically. USEPA provided guidelines for nonpotable water reuse,which stated various conventional technologies commonly used in treating municipal wastewater such as primary and secondary treatment, and specified the... 

The flow scheme of these facilities is very similar to the one of a conventional water supply facility which treats surface water (in spite of the very different use). It usually consists of a physicochemical treatment (to reduce pollution associated with the colloids that escape from the secondary clarifiers of the WWTF) and a disinfection unit (to remove pathogens and prevent health issues related to the wastewater reuse). The first treatment follows a four-stage scheme coagulation, flocculation, clarification, and filtration. Membrane technology (i.e., reverse osmosis or electrodialysis) is sometimes proposed... 

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. 

Over the past decade, water pollution control has progressed from an art to a science. Increased emphasis has been placed on the removal of secondary pollutants, such as nutrients and refractory organics, and on water reuse for industrial and agricultural purposes. This in turn has generated both fundamental and appHed research, which has improved both the design and operation of wastewater treatment faciUties. 

A notable example of controlled water reuse was utilization of secondary sewage effluent from the Back River Wastewater Treatment Plant in Baltimore by the Sparrows Point Works of Bethlehem Steel (6). The Sparrows Point plant was suppHed primarily by weUs located near the brackish waters of Baltimore harbor. Increased draft on the weUs had led to saltwater intmsion. Water with chloride concentration as high as 10 mg/L is unsuitable for many steelmaking operations. Rollers, for example, are pitted by such waters. However, treated effluent from the Back River Plant can be used for some operations, such as coke quenching, and >4 x 10 m /d (10 gal/d) are piped 13 km to Sparrows Point. This arrangement has proved economical to both parties for >40 yr. 

The El Segundo, CA, Chevron refinery takes a further step in water reuse [76]. It receives 16,300 m /day of reclaimed water to feed its boilers. Microfiltration (ME) and RO are used to treat secondary effluent from the Hyperion Wastewater Treatment Plant to provide low-pressure boiler feedwater while a second pass RO is used to produce high-pressure boiler feedwater. 

The discharge from both domestic and industrial wastewater treatment plants (for example, from activated sludge processes) has been a low-cost source of makeup for cooling systems for many years. Efforts to reuse water continue to gain momentum for environmental conservancy and economic reasons, but the fact that secondary use waters are, by definition, of a lower grade than other supply sources inevitably means an increased risk of deposition or fouling problems in the cooling system. 

Rozzi, A. et al.. Ozone, granular acHvated carbon, and membrane Heatment of secondary texHle effluents for direct reuse, Biol. Abwasserreinig Treatment of Wastewaters from Textile Processing), 9, 25, 1997. 

Semi-dead end UF/MF membranes (effective pore size of the membrane is <0.1 pm) with intermittent backwash are being increasingly used for surface water and wastewater treatment for re-use, e.g. secondary or tertiary effluent is treated for industrial, non-potable and, in some cases, potable water reuse using UF/RO (or MF/RO) plus advanced oxidation techniques such as UV disinfection and hydrogen peroxide. The process is described in detail in Chapters 2 and 4 and several examples discussed in Chapter 3. Prominent examples of advanced reclamation plants include Water Factory 21 in Cahfornia, NEWater Factory in Singapore and the Goreangab Reclamation plant in Namibia [2]. 

Modak reported that com sugar waste (reducing sugars) fi om a starch manufacturing operation is useful for sulfur dye reduction [53]. In one reported case, textile wastewater sulfide concentration was reduced from 30 to 2 ppm, with associated reduction in aquatic toxicity. An increase in BOD resulted but was easily handled by the textile wastewater treatment system, whereas the sulfide waste was not amenable to waste treatment. The zone settling velocity in the secondary clarifiers improved as a result of the decrease in sulfide, thus increasing waste treatment efficiency. Odors were reduced. The com starch manufacturer saved 12,000 on waste treatment system expansion and 2400 in operating expenses, had the waste stream not been reused [53]. 

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... 

Europe, where some municipalities process 50% or more of their water from used sources. Obviously, there is a great need to treat wastewater in a manner that makes it amenable to reuse. This requires treatment beyond the secondary processes. 

Membrane bioreactors are an option for municipal wastewater treatment when high effluent water quality is required, for example, bathing water quality, or when the receiving water body is very sensitive or when the water is to be treated for reuse. As mentioned before (see Section 9.2.5.1), the effluent quality is superior to that of secondary sedimentation. To attain a similar effluent quality by conventional treatment, effluent filtration and disinfection would be required in addition. This needs to be taken into account when comparing the cost of MBR and conventional activated sludge treatment. 

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