POLLUTION CONTROL AT T
HREE papers (1, d , PI) have traced the pollution control progress of The Dow Chemical Company during the past twenty years. The location of the Midland plant with respect to: drainage area and downstream water nswe is Shown in Figure 1. The manufacture of over four hundred chemicals in almost five hundred buildings spread over.700 acres reqhires dsjly the disnoml of some 2OO,ooO,OOO gallons of waste water, 70 tons of e, and millions of cubic feet of vented air.
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The control of waste water pollutants has progressed steadily. e required process changes bs soon as the know-how was developed. Polluted waste waters are now broadly classified as brines, clear waters, special wastes, phenolic wastes, and general organic wastes. BRINES. About one milliongallons of waste brines result. daily from%romine, calcium chloride, Epsom salts, and magnesium
.The Dow Company installed treatment equipment or d
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LARGE CHEMICAL WORKS . .-
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b b The Midland plant ofThe Dow Chemical Campany m+nufacturesover four hundred chemicals in five hundred buildings, -iring daily disposal of some 200,000,OOO gallons of waste water, 70 tons of refum, and millions of d i e feet of vented air. Waste waters an handled as foCowst (1) Brinss nm s t o d in huge ponds and released during periods of high 50w. (2) Clear waters are discharged direct to the river with careful controlof evaporator losses. (3) Speeial wastea d t for storngeOr biological treatment m a y he recbcdated, treated with active c ~ bo*, steam-distilled, and extracted or oridieed with ddorine; inorganic acid wastea nm controlled to fit puralinity of the river. (4) Phenolic wastea n m wated by acidilication, settling, eqdiization, and biological oxidation after dilution; treatment pmeass and equipment nm described. (5) Genernl &ganic wastee of 50,000,000 gallons per day are treated through a biological plant which is also dcs&. Refuse disposal consist^ of burning the burnable materials and developing fill areas for unburnable solids. A new central refuse burner is under construction. Atmospherie pollution control works toward the elimination of odors, irritant%and ae-la. Methods and pmblems a m discussed here.
Condenserl~sarekeptataminimumtopermitdirect
of these wastes to the river. SPECIAL WASTESare t h m wastee which require dling and m o t be mixed with other plant wastes. from the phenol p m a s is one of these,since it contab too-mueh salt for direct discharge to phenolic wastea and too much phenol to be included in brine wastes. This waste is now blown to rn move low boiling organics and then paaed through activated carbon towers to remove soluble or&. After thia treatment the brine is used sa chlorine d l feed or may be pumped to brine h . storage. The carbon towers are reactivated by leaching with weak caustic and water wash. The leach water and wash water are then treated through the phenolic waste system. T h i waste water reSulthg from the direct quench of cracked oil gases is one of the most di5idt wastes encountered. The quench water contains emulsified oils, suspended tars, and light oils. It is high in odor h b o l d and is saturated with gases it quenches. The soluble organics are not readily oxidized biologically., The phenols present are mostly cresols. At present this waste is recirculated through a pond system to remove oils and cool it for re-use. This system is being abandoned for atmospheric pollution and oil recovery reasons in favor of a closed system using a clarifier and a tubular-type cooling tower. The purge of 100 gallons per minute, which represents the prooeae steam condensate, will be heavily chlorinated to oxidize organics ' and break emulsions before discharge to general organic wastes. Eventually it is hoped that all of this type of cracking can he accomplished by the Thermofor catalytic process t0 eliminate the direct Water quench. manufacturing processes. This brine, ahout eight times as strong Inorganic acid wsates which are free of organics are sewered as 88%water, is stored in some 400 acres of ponds and released directly to the river, where sufficient alkalinity exists to neutralwith downof high strflow by during ize them. The limits of disposal by this method are defined by stream water users. This method of disposal requires careful the dkalinity and the river flow. control plus experience with and knowledge of river eonditiqns and wind directions. Pond dikes are made of cky.
structures. Facilities to return seepage are provided although the sheetpiled pond is very tight. During discharge periods the river immediately below is kept under 5000 p.pm. (parts per million) as sodium chloride to protect %%hlife. The water works at Ssginay and Bay City are providd withdreahwater storage capacity and bonductivity recorders 80 that stored water can be used. whik .the salt is high in the river or bay. method of brine dis$osal'waa de-
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WATERS are warm wn-
day me classed: in. this category.
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2. 573
Flow Sheet of Phenolic Wawaete Trbtment Plant ?I& ,. ..
574
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 3.
Vol. 39, No. 5
Trickling Filters
Some of the chlorinated phenolics require special treatment before discharge to the phenolic waste system. Substitution in the para position seems to render these compounds difficult to treat biologically. Small volumes of such wastes are treated by chemical oxidation or extraction after steam distillation. PHENOLIC WASTESare treated by biological oxidation. The nastes are segregated into either the weak- or strong-waste sewer systems. Weak wastes are, as a rule, the heat exchange water that may contain 1 to 5.0 p.p.m. phenol or may be intermittently polluted. The volume of this waste varies from 13.5 million gallons per day in winter to 23.5 million in summer. Strong phenolic wastes are made up of the floor washings, pump drips, still washings, mother liquors, and vent scrubbers from all phenolic product plants. This waste averages about 1,.5 million gallons per day \\ith a phenolic concentration of 700 p.p.m. The installation of tubular condensers on barometric jets has been found a very effective control measure. Condensate can be reused in the process as a rule. One of the most important units in phenolic pollution control is the strong-waste storage pond. It is necessary that the strong phenolic wastes be acid so that the higher substituted phenolics will be settled out in the pond. Dow's 30-acre 45,000,000-gallon pond serves to settle precipitated phenolics, equalize waste concentrations and flows, and provide for variable feed to treatment process by virtue of storage. After ponding, the strong phenol waste is mixed with weak R-aste and neutralized to prepare for treatment by biological oaidation. The first unit in this process (Figure 2 ) is the mixing chamber, pump house, and laboratory. The mixed waste is pumped to the 140-foot diameter clarifier and thence to the trickling filters, the artivated sludge plant, and the effluent ponds. The mixed waste is neutralized iJ-ith lime, when necessary, to maintain a pH between 6.1 and 7.5. Prolonged periods of high causticity or acidity necessitate by-passing the entire weak waste flow to the general
plant wastes, 1% here neutralization is accomplished by virtue of larger flows of alkaline water. During such times the strong phenol ryaste is stored in the ponds. A motor-controlled by-pass line is provided on the mixed-waste force main so that it is possible to divert mived waste to the strongv aste pond during periods of high phenol concentration in weak wastes. The clarifier at this plant serves to skim light oils and settle heavy oils and precipitates to prepare the wastes for the filters. The tank is 140 feet in diameter with an 8-foot side xall depth and a 13-foot center depth. A two-arm Dorr mechanism scrapes the Judges to a hopper at the center, from which they are pumped to the sludge lagoon in a corner of the strong waste pond. The four trickling filters (Figure 3) are 142 feet in diameter on top nith the 2.5-3.5 inch blast furnace slag media forming the outside wall on a 45' slope, which makes the bottom diameters 162 feet. The center gallery and complete bottom coverage of ,Irmcre tile were designed to give mavimum aeration (Figure 4).
Figure 4.
Center Gallery of Trickling Filter
May 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 5 .
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Activated Sludge Plant
I\Iotor-driven tro-arm distributors are of 10-inch pipe with 8inch pipe for the last 10 feet. Water head on t,hese units is sufficient, t,o rotate them so that t'he motor serves as a speed regulator most of the time. The temperature of the mixed waste leaving these filters varies from 53" t o 95" F. The pH of the mixed liquor is kept above 6.1 and below 8.0. The phenol concentration for normal feed varies betn-een 30-50 p.p.m. Concentrations higher than that are recirculated. The beds average 9.75 feet deep and obtain removals of phenol from 4.29 pounds per 1000 cubic feet at 56" F. to 9.0 pounds per 1000 cubic feet at 83" F. with a feed rate of 10.2 million gallons per acre per day. Removal of B.O.D. (biochemical oxygen demand) varies from 15.8 pounds per 1000 cubic feet, to 27 pounds per 1000 cubic feet at the respective temperatures given. The first two of these beds have been in operation eight years, t'he second pair five years. They have served and continue to serve as effective oxidation units. The faces of the stone in contact, with wat,er are covered with a slime containing millions of bacteria which feed on the carbon of the dissolved organic matter and the oxygen of t,he water. The oxygen is derived from air passing t,hrough the beds countercurrent to the Tvater. The activated sludge plant (Figure 5 ) receives the filter effluent and excess ~ e a waste k through a grit chamber. Return sludge is mixed with inflow at the effluent end of the grit chamber, and the flow is directed to each of the five parallel batteries. One battery is comprised of three mechanical aerators and two to four jet aerators in series in a 24 X 75 foot tank with 15-foot water
depth, followed by a 24 X 70 X 10 foot setrling tank. Thc, rtiturn sludge consists of the settled, flocculated bacterial slimw. I n the filters the water was passed over the bacteria, whereas her
