HOW MUCH DOES NITROGEN CONTROL COST? 1 IK- chart (right) shows the approximate nal ioiuil average lotul cosls, including plant ainoi i i/ation (25 years ul 6 percent), oper- aiion and nuiinienanee lor biological ni- n ogcn conirol i ne ill oils. Costs tor nitrogen removal by breakpoint chlorination (in addition to cosls for conventional treal- meni ) are constant at approximately 6c'/ I 000 gallons Mealed. Cosls for amnionia- sitipping and ion-exchange can vary sig- inlicanlly depending on plant si/e and location, availability of materials, etc. A detailed investigation must therefore be made to determine exact costs for these two physical-chemical methods of remov- ing nitrogen from waslewaler. WHERE IS CONTROL OF NITROGEN IN WASTEWATER BEING APPLIED? 1 25 50 Plain Size (Million Ga 75 10 Ions per Dayl A. Conventional Treatment ("Ins Nitrification 1'lus Denitrifiailion K. Conventional Treatment Plus Nitrification ('. Conventional Treatment This is a partial listing of full-scale nitro- gen control treatment plants under design. construction or operation. Washington, 1). C. 1 ampa. Horida Alexandria. Va. Salt Cieek (Chicago). III. A i ling! on. Ya. Madison. Wise. Ian lax County, Va. Him. Mich. \\ankeegaii. III. Highland Park, 111. (itirnce, 1II. Jackson. Mich. ()i atme Count \ . Calif. lienton Harbor. Mich. Ovvosso. Mich. Central Contra C'osta. Calif. Rosemonl. Minn. H I am>. Texas How (Million Gallons/Day) .soil 60 54 50 .;o 30 22.5 20 20 18 17 17 15 13 6 Type Facility Suspended Growth System Fixed Film Denilrification Ion-Exchange F'i.xed Film Denitrificalion Breakpoint Chlorinaiion Nitrification Ion-Exchange Nitrification Nitrification Nitrification Nitrification Nitrification Ammonia Stripping Nitrification Breakpoint Chloiinalion Suspended Growth System Ion-Exchange Fixed Film Denilrification WHERE CAN I GET MORE INFORMATION? ( ontacl your consulting engineer nr write to: Environmental Protection AgencA '-. Technology Transfer Washington, D.C. 20460 ------- HOW CAN NITROGEN IN WASTEWATER BE CONTROLLED? Ammonia nitrogen can lie reduced in con- centration or removed I rom waste water by several processes. These processes can be di- vided into I wo broad categories: biological methods and physical-chemical methods. BIOLOGICAL METHODS One meth- od of ensuring a low ammonia content in treated wastewater diluents is to induce nitrification to occur in the treatment sys- tem. Nitrification is merely the biological conversion ol nitrogen in the lorui ol am- monia to nitrogen in the form of nitrate. Nitrification is accomplished by providing that amount of oxygen required in the bio-chemical reaction which converts am- monia nitrogen to nitrate nitrogen. This is roughly 4.5 pounds of oxygen per pound of ammonia nitrogen in the wastewater. '•.quipment required consists basically of tank through which the wastewater to e nitrified passes, and oxygen or air gener- ing. pumping, and diffusion equipment. When the effluent from a wastewater eatment plant is discharged to a recciv- g water with a significant flow, such as •'ivcr. nitrate nitrogen may not have any rerse effects upon it. In fact, a nitri- ii-il effluent free of substantial quantities of ammonia can oiler several advantages: I. Nitrate nitrogen provides oxygen to sludge beds and prevents the forma- tion of septic odors 2. A nitrified effluent contains less sol- uble organic material than the same effluent before nitrification 3. Nitrified effluents are more ef- ficiently disinfected by chlorine treatment 4. A nitrified effluent reduces the oxy- gen demand on the receiving waters The deciding factor in determining whether the discharge of a nitrified ef- fluent to a free-flowing receiving water is acceptable is the level of nitrate nitro- gen contained in it. If it is loo high, then further action is necessary to control the nitrogen content ol the el fluent. This is also the case when treated waslewater is discharged to relatively still bodies of wa- ter such as lakes, reservoirs, and estuaries. In these cases even a highly nitrified ef- fluent can have harmful effects, such as fostering algal blooms. If a nitrified effluent is determined un- acceptable, there arc two steps which can be taken. Each of these steps involves dcnitrification the conversion of nitrate nitrogen to nitrogen gas. 1. Suspended Growth Dcnitrification. In this form of dcnitrification. nitrified wastewater Hows to a tank where an or- ganic compound (such as methyl alcohol) is added in proportion to the amount of nitrate nitrogen present. The end products of the reaction induced in this tank are nitrogen gas and carbon dioxide, both of which are liberated to the atmosphere. 2. Fixed Film Dcnitrification. As in suspended growth denitrification. an or- ganic compound is added to the nitrified wastewater. However, in this form of de- nitrification, the nitrified wastewater and organic compound passes through a col- umn of fine media such as sand. Denitri- fying bacteria are produced and attach as a slime to the media surface. The end pro- ducts again are nitrogen gas and carbon dioxide, which are released to the atmos- phere. Fixed-film denitrification has the added benefit of filtration, and under nor- mal circumstances will produce an effluent low in suspended solids concentration. Biological Methods of Controlling "•';* Primary Secondary ------- PHYSICAL-CntMICAL METHODS There aie several other means of removing nitrogen from wastewater—all of which are physical-chemical rather than biologi- cal. They are: 1. Ammonia-Stripping. The ammonia nitrogen which, as mentioned previously, is present in wastewater during conven- tional biological treatment can be removed by a physical process called desorption or, more commonly, "stripping." Simply stated, the wastewater is first made very alkaline by adding lime, and the ammonia is then induced to leave the water phase and enter the gas phase where it is re- leased to the atmosphere. To accomplish tliii stripping, the wastewater is merely contacted with a sufficient quantity of vnonia free air. This contacting with air is done in a slat-filled tower very simi- lar to those used in industry to cool water. It should be pointed out that ammonia- stripping is limited to warm weather areas with little or no prolonged freezing. Also the impact of ammonia discharge on the surrounding environment must be eval- uated on a case-by-case basis. 2. Breakpoint Chlorination. Chlorine added to wastewater reacts with the am- monia nitrogen ti m nitrogen gas. This may be the simplest i itrogen removal pro- cess, but it has sonn disadvantages. One of these is the amount of chlorine re- quired—approximately 10 parts of chlo- dlfcViic Compound Wastewater ation Fixed Film System Denitrification rine to remove one part of ammonia. Therefore, a city of 100,000 would require approximately 6 million pounds ot chlo- rine per year (abotit 30 times that required for normal disinfection purpo'ses). The transportation and handling problems are obvious. Another possible disadvantage is that this large dose of chlorine may re- sult in the formation of chlorides which would have to be eliminated by subse- quent demineralization. 3. 1'on-Exchange. This nitrogen remov- al process involves passing ammonia-laden wastewater through a series of columns packed with a material called clinoptilo- lite. The ammonium ion adheres to or is absorbed by the clinoptilolite. When the first column in series loses its ammonia adsorptive capacity, it is removed from the treatment scheme and washed with limewater. This step converts the captured ammonium ions to ammonia gas, which is then released to the atmosphere by con- tacting heated air with the wastewater stream, much the same as described pre- viously under ammonia stripping. A. Wastewater Inlet B. Regenerant Inlet C. Regenerant Dit'fuser D. Clinoptilolite E. Underdrain System I . treated Wastewater ------- Nitrogen in its many forms has long played a fundamental role in the aquatic environ- ment. It is now apparent that ecological imbalances in the natural environment have been caused, in part, by the exces- sive discharges of nitrogenous materials to natural waterways. Along with phospho- rus, nitrogen occupies a critical role in the eutrophication of lakes. In certain forms nitrogen is one of the major nutrients sup- porting blooms of green and blue-green algae in surface waters. In addition to the nutrient value of nitrogen, the oxygen demand of nitrogen forms can represent as much as 70% of the total oxygen de- mand of conventionally treated munici- pal wastewater. During conventional biological waste- water treatment, almost all the nitrogen contained in the wastewater is converted into the ammonia nitrogen form. Al- though ammonia has very little toxicity to humans, treated wastewater effluent containing ammonia has several undesir- able features: 1. Ammonia consumes dissolved oxy- gen in the receiving water 2. Ammonia can be toxic to fish life 3. Ammonia is corrosive to copper fittings 4. Ammonia increases the amount ot chlorine required for disinfection ------- |