Primary Treatment System

Primary treatment is necessary to protect the downstream oil-water treatment system from being overloaded. Basic primary treatments include skimming and gravity separators. Skimming is widely used as the fundamental method to remove floatable oil from the surface of wastewater. It is the primary process considered in selecting separation 

Skimmers may equipped in different ways such as free floating, built into a vessel, side mounted on a vessel, or held by crane. Several types of skimmer may be used for oil removal. The rope skimmer is one type that employs polypropylene, PVC, or aluminum as adhesion materials, as shown in Fig. 3. The floating oil can be attached to these moving surfaces and removed out of the water. The belt skimmer (Fig. 4) is used to convey floating oil by moving through the oily waste from water. In a filter skimmer, the water can pass through the belt while the oil is filtrated and adhered on the belt. At the top of the belt the oil is scarped off into a sump or a pump. 

The coalescent principle becomes the significant principle for small-oil-droplet removal. When the droplets coalesce, they do not form floes as the solid particles can, but coalesce into larger droplets. Interfacial or surface tension of the liquid tends to make the droplets from spherical shapes, which follows the assumption of Stokes s law mentioned previously. With coalescent principle, the Stokes s law can be applied. The coalescent technique widely used in oil droplet removal is the plate separator. 

The plate separator is a major configuration of gravity separators. This equipment uses differences in densities between oils and water as a principle separation technique. The module can be a single plate or three plates or may contain a nest of parallel plates, which is typically 10-20 mm wide. The operational principles of plate separators are to allow oil droplets rise to a plate surface where coalescence can occur and to form larger oil droplets, which are easier to separate. The performance of the plate separator can be enhanced by selecting appropriate plate designs or by the use of a coalescer. 

A parallel plate separator is a modified type of plate separator using the same mechanism as the conventional gravity separators. The effectiveness of this separator is increased by installation of parallel plates in the separation chamber, without requiring 

---

The vendor states that MRRP may not be cost effective for contaminated water or wastewater as a primary treatment system but could recover mercury from carbon systems used to treat these waste streams. According to the Gas Technology Institute, the mobilization and demobilization of mobile thermal treatment systems can be costly and time consuming. These technologies are often energy intensive. 

The capital cost of most aqueous waste treatment operations is proportional to the total flow of wastewater, and the operating cost increases with decreasing concentration for a given mass of contaminant to be removed. Thus, if two streams require different treatment operations, it makes no sense to mix them and treat both streams in both treatment operations. This will increase both capital and operating costs. Rather, the streams should be segregated and treated separately in a distributed effluent treatment system. Indeed, effective primary treatment might mean that some streams do not need biological treatment at all. 

In order to conform to environmental quaUty guidelines, mills have installed a number of primary and secondary treatment systems to control... 

Small Communities. Small communities and recent subdivision additions to larger communities, which have not yet been coimected to municipal coUection systems, must have a means of waste disposal. Septic tanks are a possibiHty, but require periodic servicing and cleaning. Furthermore, the soil is not always suitable for accepting the effluent. An alternative is the package plant. These units are commercially produced to serve small areas. They furnish primary treatment and some secondary treatment, and require only minimal operating supervision. Capacity can be varied as needs dictate. In general, pubHc health authorities prefer such installations instead of septic tanks. 

When organics containing reduced nitrogen are degraded, they usually produce ammonium, which is in equilibrium with ammonia. As the pK for NH3 NH4" is 9.3, the ammonium ion is the primary form present in virtually all biological treatment systems, as they operate at pH < 8.5 and usually in the pH range of 6.5-7.5. In aerobic reactions, ammonium is oxidized by nitrifying bacteria (nitrosomonas) to nitrite... 

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). 

Figure 21.8 shows a typical sequence of the major equipment systems in a wastewater treatment plant.36 The function of primary treatment is to remove suspended solids from the wastewater, and then to remove organic materials by biological secondary treatment. Primary treatment processes used by kraft mills typically involve screening followed by either sedimentation or flotation.40... 

The primary distinguishing feature of the improved activated sludge treatment system is that high-rate DAF is the secondary clarifier for separation of suspended solids from the activated sludge aeration basin effluent, as opposed to secondary sedimentation alone in a conventional activated sludge system. 

The competitive physical/chemical system that is being installed at Rosemount, Minn., consists of primary treatment followed by coagulation, sand filtration, activated carbon adsorption, another filtration step, ion exchange, and oxidation. This can produce a highly purified water at less cost than a system involving primary, secondary, and tertiary treatment.30... 

The study of osteoclast differentiation is important for understanding potential new treatments for osteoporosis. Such therapies are typically explored in tissue culture models such as the Raw264 mouse monocytic cell line, which is capable of differentiation into functional multinuclear osteoclasts after treatment with the cytokine Rankl. Use of transformed cell lines raises the concern that results may not be extrapolated to normal tissue. To address this question, the transcriptional responses for Rankl treatment of the Raw264 cell line, and of two ex vivo primary cell systems (bone marrow macrophages, and hematopoetic stem cells) were compared using Affymetrix GeneChips [23]. The models proved to... 

It is not known whether this process would be competitive with the lime/soda precipitation process for primary treatment. For new plants, the main issue is capital cost. The lime/soda process is relatively inexpensive for large-scale plants. For small plants, the BDFI system may be competitive, particularly for packaged turn-key plants, if installation and start-up costs are taken into consideration. The BDH system is very compact and can be quickly started and easily operated with minimal labour requirements. 

Upon release to surface waters, di- -octylphthalate is expected to partition mainly to sediments and to suspended particulates. In a pilot-scale waste-water treatment system, di- -octylphthalate partitioned mainly to primary treatment sludge (Petrasek et al. 1983). The compound strongly adsorbs to organic matter contained in soils and sediments adsorption is probably the most important transport process for the... 

Any treatment process that can remove the toxicity-causing constituents can reduce whole-effluent toxicity of a discharge. If the primary cause of effluent toxicity can be identified through the TIE or TRE procedures, specific treatment processes can be incorporated into the existing treatment system to control the toxicity. However, for a complex wastewater such as that from refinery and petrochemical facilities, the cause of toxicity may not be easily identified. The toxicity can be caused by a combination of constituents that exhibit synergistic or antagonistic effects. 

Since 1990, several new or revised U.S. environmental regulations, which significantly affect refinery wastewater treatment systems, have been promulgated. The most important ones include the revised Toxicity Characteristics (TC) rule, the Primary Sludge rule, and the Benzene NESHAP (National Emissions Standards for Hazardous Air Pollutants) rule. These regulations and their impacts on refinery wastewater facilities are briefly discussed below. 

---