Nitrate removal from water by biological denitrification

Abstract

Ground water pollution by nitrate from routine agricultural practices is a common and growing problem in the major agricultural areas of the world. The concentration of nitrates in these areas may exceed the maximal limited value (MLV for nitrates 50 mg/L). Nitrate removal has been successfully achieved with the use of several processes: ion exchange processes, reverse osmosis combined with membrane technology and extraction combined with electrodialysis. All the mentioned processes have been effectively applied and implemented on the treatment plants. The common disadvantage of all the applied processes is the final production of concentrated waste, contaminated with nitrates. The waste as by-product requires additional treatment and removal. Biodenitrification is a promising alternative technique for the removal of nitrate from drinking waters. The major advantages of biological denitrification is its simplicity, low-cost and complete removal of nitrate without waste production, since the final product of the process is nitrogen. The majority of biodenitrification relies on heterotrophic bacteria that require an organic carbon source and anoxic conditions for the first stage of process. Since the drinking water has a low carbon content an additional carbon source is required. Carbon source can be an external reservoir of methanol, ethanol, organic acid or hydrogen. The process of biological denitrification is typical for waste water treatment but some analysis and studies show that it is possible to apply this process for nitrate removal from drinking water. In this paper a possibility for the use of biological denitrification for removal of nitrate from drinking water has been discussed and a concrete water treatment plant for denitrification of groundwater in Česnikovo, Poland has been presented.

U područjima kod kojih je poljoprivredna aktivnost značajna sadržaj nitrata u podzemnim izvorima vode može biti i iznad dozvoljenih vrednosti prema propisima za vodu za piće (MDK 50 mg/L). Uklanjanje nitrata iz vode do sada uspešno je primenjeno postupcima: jonske izmene, reversne osmoze uz membransku tehnologiju i ekstrakcije uz elektrodijalizu. Navedeni postupci primenjeni su i na postrojenjima, ali uočen je zajednički nedostatak, nastanak koncentrovanog otpadnog materijala koji zahteva dodatni tretman ili uklanjanje. Alternativa navedenim tehnologijama jeste biološka denitrifikacija. Biološka denitrifikacija je relativno jednostavan, jeftin proces za potpuno uklanjanje nitrata, uz oslobađanje azota, bez nastanka otpada. Srž procesa biodenitrifikacije čine heterotrofne bakterije kojima su neophodni anoksični uslovi. Voda za piće ne sadrži dovoljno organskog ugljenika, koji obezbeđuje anoksične uslove. Spoljni izvor organskog ugljenika može biti metanol, etanol, sirćetna kiselina, ili vodonik. Proces biološke denitrifikacije tipičan je za pripremu i tretman otpadne vode, međutim ispitivanja sa vodom za piće pokazuju da se uz pravilno primenu ovaj postupak može koristiti i za pripremu vode za piće. U radu je prikazan pregled metoda za uklanjanje nitrata, prednosti i nedostaci određenih postupaka, kao i primer postrojenja za denitrifikaciju podzemne vode za naselje Česnokovo, u Poljskoj.