Assessment of corrosive characteristics of water according to indices of water aggression: Example of well field in Vojvodina

Abstract

For the assessment of aggressiveness and corrosiveness of water many indices have been developed and some of them are presented in this paper. Although number of indices has been developed indexes none of them has been able to accurately quantify and predict corrosiveness of water or aggression. Indexes can be used as indicators of possible corrosiveness of water. Samples of raw water from four wells in Vojvodina, which are supposed to make a one-well field, have been analyzed in this paper. The assumption is that the water will be treated with filtration and disinfection before being introduced in to the system. The analysis was conducted using Langelier Index of Saturation, Ryznar Index, Puckorius Scaling Index, the Aggressiveness Index, Larson-Skold's Index and Modified Larson-Skold's Index. Most often, the development of corrosion can be seen through: deterioration of the pipes (measured by the loss in mass of pipes and oxygen consumption), the formation of deposits (measured by hydraulic loss or the buildup of deposits) and change in water quality in the system (measured by the concentration of iron, change of color and turbidity). The key water quality parameters that affect the corrosion processes are: pH, alkalinity and buffering capacity. Among the best known indices, which the aggression and corrosion properties of water express by CaCO3, are: Langelier Index of Saturation (LSI), Ryznar Index (RSI), Puckorius Scaling Index (PSI), and the Aggressiveness Index (AI). In addition to these indices, which observe the possibility of corrosion by CaCO3, other indices have been developed that take into account other parameters of water quality and their effect on corrosion of the pipe distribution network. Most common among the Larson-Skold's index (LR) and modified Larson-Skold's index (LRM). A sample from the well K3 has about the same values of LSI, RSI and PSI index as the samples from wells E1 and L2, but much worse values of LR and LRM index, which indicates that water from wells K3 has a greater potential to cause corrosion problems and the problems of water. It is recommended that water from wells K3 is not used for water supply. Assuming that the wells have the same capacity, an analysis of the indices of water that would have been a mixture of all four wells (mixture M1) and the water is a mixture of wells P2, E1 and L2 (mixture M2), has been conducted. Based on the analysis of a mixture of water M1, which includes water from all 4 wells, and mixtures M2, which uses water from wells P2, E1 and L2, negative impact water from wells K3 has been shown. According to all parameters, a mixture M1 showed a greater tendency to develop corrosion than mixture M2.

Za procenu agresivnosti i korozivnosti vode razvijeni su indeksi pokazatelja korozivnosti vode, od kojih su neki predstavljeni u ovom radu. Indeksi mogu da posluže kao indikatori korozivnosti vode. U ovom radu analizirani su uzorci sirove vode iz četiri bunara u Vojvodini za koje se pretpostavlja da čine jedno bunarsko polje. Pretpostavka je da će voda biti obrađena fitracijom i dezinfekcijom pre puštanja u mrežu. Analiza je rađena pomoću Langelierov indeksa zasićenja, Ryznarovog indeksa, Pukoriusovog indeksa za korozione slojeve, indeksa agresivnosti, Larson- Skold-ov indeksa i modifikovanog Larson-Skold-ov indeksa. Najčešće se razvoj korozije može sagledati kroz: propadanje cevi (meri se gubitak mase cevi i potrošnja kiseonika), formiranje naslaga (mere se hidraulički gubici ili stvaranje naslaga) i promenu kvaliteta vode u sistemu (meri se koncentracija gvožđa, određuje boja i mutnoća). Ključni parametri kvaliteta vode koji utiču na korozione procese su: pH vrednost, alkalitet i puferski kapacitet. Među najpoznatijim indeksima, koji agresivnost i korozione karakteristike vode izražavaju putem CaCO3, su: Langelierov indeks saturacije (LSI), Ryznarov indeks (RSI), Puckoriusov indeks skaliranja (PSI), indeks agresivnost (AI). Pored pomenutih indeksa, koji mogućnost korozije sagledavaju preko CaCO3, razvijeni su i drugi indeksi koji uzimaju u obzir i druge parametre kvaliteta vode i njihov uticaj na koroziju cevi distributivne mreže. Među najpozantijim su Larson-Skoldov indeks (LR) i modifikovani Larson-Skoldov indeks (LRM). Uzorak iz bunara K3 ima približno iste vrednosti LSI, RSI i PSI indeksa kao i uzorci iz bunara E1 i L2, dosta lošije vrednosti LR i LRM indeksa, ukazuju na to da voda iz bunara K3 ima veći potencijal da izaziva koroziju i probleme sa bojom vodom . Preporuka je da se voda iz bunara K3 ne koristi za vodosnabdevanje Pod pretpostavkom da bunari imaju jednaku izdašnost, urađena je analiza indeksa korozivnosti za vodu koja bi bila mešavina iz sva četiri bunara (mešavina M1) i voda koja je mešavina bunara P2, E1 i L2 (mešavina M2). Na osnovu analize mešavina vode M1, koja uključuje vodu iz sva 4 bunara, i mešavine M2, koja koristi vodu iz bunara P2, E1 i L2, pokazan je negativan uticaj vode iz bunara K3. Prema svim parametirma, mešavina M1 je pokazala veću tendenciju za razvoj korozije od mešavine M2.