Surface water, turbidity

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

Most surface waters contain varying amounts of suspended solids, including silt, clay, bacteria, and vimses and it is necessary to remove these before to distribution to the domestic or industrial consumer. Suspended soHds not only affect the acceptabiUty of the water but also interfere with disinfection. The principal treatment processes are sedimentation (qv) and filtration (qv). Sedimentation alone is rarely adequate for the clarification of turbid waters and is of htde or no value for the removal of such very fine particles as clay, bacteria, etc. Table 1 shows the effect of particle size on the sedimentation rate of a soHd having a specific gravity of 2.65 in water at 20°C. 

For turbidity, color and microbiological control in surface water treatment filtration. Common variations of filtration are conventional, direct, slow sand, diatomaceous earth, and membranes. 

Surface water half-lives for removal from water column at 25°C in midsummer sunlight were, t,/2 = 10.5 h for deep, slow, somewhat turbid water t,/2 = 21.6 h for deep, slow, muddy water t,/2 = 8.5 h for deep, slow, clear water t,/2 = 3.5 h for shallow, fast, clear water and t,/2 = 1.4 h for very shallow, fast, clear water (Southworth 1977, Herbes et al. 1980) ... 

To test for volatility in steam, heat a small sample of the substance to boiling (porous pot ) in a test tube with about 2 c.c. of water and hold the bottom of a second test tube containing some ice in the issuing vapours until a drop of water has formed on the cold surface. A turbidity in the drop indicates that the substance is volatile with steam. 

The availability of DSi can regulate the composition of phytoplankton species (Kilham, 1971 Officer and Ryther, 1980 Egge and Aksnes, 1992). For example, diatom growth is dependent on the availability of DSi to nondiatom phytoplankton species which are Si independent. DSi uptake by diatoms can even occur in bottom waters or turbid surface water where light may be limiting (Nelson et al., 1981 Brzezinski and Nelson, 1989). However, once the supply of DSi has diminished diatom production will decrease and diatoms will be replaced by other phytoplankton species. Limitation of DSi in Chesapeake Bay resulted in a rapid decline in diatoms and an increase in cyanobacteria (Malone et al., 1991). Similarly, an estimated 50% decline in DSi from the 1950s to the 1980s in the Mississippi River (Turner and Rabalais, 1991) resulted in DSi limitation for diatoms on the... 

Carry-over and overfed of alum (aluminum sulfate) coagulants, post-precipitation of alum coagulants due to poor pH control, and naturally-occurring aluminum silicates are responsible for aluminum fouling of RO membranes. Alum feed is usually employed on surface waters where clarification is the first pretreatment step. The overfed of alum occurs when the raw water turbidity increases. Many operators will continue to add alum past the point called for by stoichiometry. Carry over occurs when the clarifier is not operated properly. 

The term settleable solids applies to suspended solids that settle under quiescent conditions because of the influence of gravity. Their measurement is important in engineering practice to determine the need for sedimentation units and the physical behavior of waste streams entering natural water bodies. Colloidal particles do not settle readily and cause the turbidity found in many surface waters. 

There is abundant evidence from culture studies that both AOB and NOB are photosensitive. It is a high priority to investigate the photosensitivity of AOA. Even if aU nitrifiers exhibit photoinhibiton in some form, however, the direct and indirect ecological imphcations of this physiology for the rates and distributions of nitrification in the environment are not easily predicted. Dissolved organic matter in seawater, as well as turbidity due to sediments or phytoplankton, might aU provide photoprotection in surface waters, and regulation of nitrification by other factors discussed in this section may be much more important in many environments. 

Colloids tend to be most abundant in reducing groundwaters and turbid surface waters. In clear groundwater samples which have been filtered naturally by movement through an aquifer, differences between concentrations in filtered and unfiltered aliquots are often relatively small. 

Diatomaceous earth filter plants have been chosen for projects with limited initial capital, and for emergency or standby capacity to service large seasonal increases in demand. Because these systems are most suitable for applications where influent is low in turbidity and bacterial counts, water supplies presently receiving just chlorination may consider using diatomaceous earth to meet the filtration requirements of the Surface Water Treatment Rules (SWTR) (2). 

Diatomaceous earth filtration is a well-established water treatment process. It performs well on groundwater with high concentration of iron and manganese, or on surface waters with low influent turbidity, acceptable color, and bacteria levels. Effective removals of viruses and Giardia range up to 99.95% and from 99% to 99.99%, respectively. 

---