TITLE: INVESTIGATION OF THE PRESENCE, SPECIATION, DOMINANCE AND IMPACT OF DISINFECTION BY PRODUCTS IN DRINKING WATER AND WASTEWATER

Author: K.L Mukwevho

Company

Johannesburg Water SOC Ltd

P O Box 61542, Marshalltown, 2107, RSA

Email:

Phone: 011728 7373

Abstract

This work investigates if disinfection by products are formed, which species are formed, how this species are distributed, at what concentrations are they present, if their concentration pose any risk to human and environment. It also investigates precursors which influence the formation of this disinfection by product and amongst those precursors which was responsible for their formation, speciation and dominance. The study was conducted using final effluents of Northern Wastewater treatment Works, Bushkoppies Wastewater Treatment Works both Johannesburg Water plants and Tap water from one of the taps in Northern Works laboratory. Samples were taken over a period of four month from October 2012 to January 2013. Fifteen samples for each were tested for Total organic carbon (TOC), residual chlorine, pH, temperature, haloacetic (HAA) acid, chloroform, bromodichloromethane, dibromochloromethane and bromoform. Chloroform, bromodichloromethane, dibromochloromethane and bromoform are collectively called Trihalomethanes (THMs).Results were presented in graphs and tables. Obtained averages of disinfection by products were compared with maximum permitted contaminant level from South African Bureau of Standards guidelines and Florida Environmental Protection Agency guideline.

Haloacetic acids were not found but THMs were found in both wastewater and drinking water. Chloroform was the dominant species in both Northern and Bushkoppies Wastewater effluents. The distribution pattern in both effluents was the same. Therefore concluded that the type of organic matter was the responsible precursor in the speciation and dominance of THMs formed in wastewater effluent. In tap water there was a balance presence of bromated THMs and chloroform found. Therefore concluded that chlorine-bromide ratio was equal and was the responsible precursor for the speciation and dominance of THMs formed. The levels of THMs found in both wastewater effluents and drinking water were lower than lower than the maximum permitted contaminant level in the Florida Environmental Protection Agency and South African Bureau of Standards therefore the discharged effluent is safe for the environment and tap water safe for human consumption.

The of this study was to establish if disinfection by products (DBPs) are formed, how they are speciating, which of the DBP is dominant, which precursor is responsible for their presence and dominance and if their current levels pose any health risk

  1. Introduction

Disinfection is a process where chemicals are intentionally added to inactivate disease causing bacteria in drinking and wastewater (Edward, J.K.2011).Different disinfectant results in different DBPs. For the purpose of this study, focus will be on DBPs formed by disinfectant used at Bushkoppies Wastewater Treatment Works and Northern Wastewater Treatment Works and Rand Water Plants, because Bushkoppies Wastewater Treatment Works and Northern Wastewater Treatment Works finaleffluents (BFE and NFE) and tap water samples were used. Bushkoppies Wastewater Treatment Works and Northern Wastewater Treatment Works are both owned by Johannesburg Water. Bushkoppies Wastewater Treatment Works and Northern Wastewater Treatment Works usecalcium hypochlorite (Makoane. et al) and Rand Water uses chlorine gas (Nkomo, A.) disinfectants.

Calcium hypochlorite [Ca(OCl)2] and chlorine gas(Cl2) dissociate and ionise in water to form hypochlorous acid which reacts with organic matter to form DBPs. In the presence of bromide, hypochlorous acid reacts with bromide to form hypobromous acid which further reacts with organic material to form bromated DBPs. Following these are the reactions

Ca(OCl)2+ H2O → Ca(OH)2 + 2HOCl

Cl2 + H2O → 2HOCl + H+ + Cl-

HOCl + organic matter → DBPs (Ivahnenk, T. et al)

HOCl + Br- → HOBr + Cl-

HOBr + organic matter → bromated DBPs (Yeats, S. et al).

The DBPs of high concern formed from calcium hypochlorite and chlorine gas are Trihalomethanes(THMs) and haloacetic acid (Lantagne D.S et al).THMs is a collective name for four compounds namely chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3).

The quantity and speciation of THMs and HAA depends on the type and concentration of organic matter, temperature, pH and concentrations of chlorine and bromine (Ivahnenk, T. et al). The above mentioned parameters were analysed at Cydna, Goudkoppies and Northern Works accredited chemistry and water laboratories

The speciation and dominance of THMs depends on the concentration of bromide and chlorine (Yeats, S).

Chloroform will dominate when there is no bromide. Bromated THMs (bromodichloromethane and dibromochloromethane) will be present when the concentration of bromide is between 0.16-0.8mg/ℓ. Bromoform will dominate when the concentration of bromide is above 2.4mg/ℓ.

The speciation and dominance of THMs was characterised according to DBPs abundance classification Model (Edzwald, J.K).

* Very high - when their concentration above 100 μg/ℓ.

* High – when their concentration is between 10-100 μg/ℓ .

* Medium – when their concentration is between 1-10 μg/ℓ.

* Low – when their concentration is below 1μg/ℓ.

The organic matter found in wastewater is different from drinking water supplies and for this reason the findings will not be compared against each other.

The risks to human was classified by comparing determined tap water THMs and HAA averages against South African Bureau of Standard (SABS) maximum permitted contaminant levels. The risk to the environment was classified by comparing determined effluents THMs and HAA average against Florida Environmental Protection agency (FEPA) maximum permitted contaminant level.

  1. Results

Fig1

Fig2

Fig3

Fig4

Table1: Distribution and Dominance (Edzwald,J.K)

SAMPLES / CHCl3 / CHBrCl2 / CHBr2Cl / CHBr3
T-Water / HIGH 58% / HIGH
33% / MEDIUM 8.2% / LOW 0.35%
NFE / HIGH 82% / MEDIUM 16% / LOW
2.2% / LOW 0.01%
BFE / HIGH 81% / MEDIUM 17% / LOW
1.9% / LOW 0.01%

Table2: Risk in tap water against SABS 241 Class1 drinking water.

T-Water / AVERAGE (μg/ℓ) / SABS (MCL) (μg/ℓ) / RISK PROFILE
CHCl3 / 47 / - / SAFE
CHBrCl2 / 26 / - / SAFE
CHBr2Cl / 6.4 / - / SAFE
CHBr3 / 0.3 / - / SAFE
TOTAL THM / 80 / 200 / SAFE
HAA / NOT found / 70 / SAFE

Table3: Risk of Wastewater against FEPA

DBPs / NFE / BFE / FEPA / RISK Profile
CHCl3 / 17 / 33 / 470 / Safe
CHBrCl2 / 3.4 / 7 / 22 / Safe
CHBr2Cl / 0.5 / 0.7 / 34 / Safe
CHBr3 / 0.001 / 0.005 / 360 / safe
HAA / Not found / Not found / - / safe
  1. Conclusion

•DBPs are formed in both wastewater and drinking water.

•There was a balance presence of bromated THMs and chloroform in tap water therefore the concentration of chlorine and bromide was responsible for the speciation of THMs formed.

•Individually chloroform was dominant in tap water.

•Much as Bushkoppies and Northern Wastewater Treatment Works have equal concentration of TOC they did not yield equal levels of THMs but they both produced same pattern and percentage of THMs species.

•That could only mean both treatment works contain the some type of organic material because it behaved in the same way when it entered in a chemical reaction.

•Therefore we can conclude that the type of organic matter was responsible for the speciation and dominance of THMs in wastewater effluent.

•Chloroform is the dominant species (> 80%) in wastewater effluent.

•Compared to SABS and FEPA the levels of DBPs formed in both tap water and wastewater effluents were low. Therefore our water is safe for the environment and to human.

•That could only mean both treatment works contain the some type of organic material because it behaved in the same way when it entered in a chemical reaction.

•Therefore we can conclude that the type of organic matter was responsible for the speciation and dominance of THMs in wastewater effluent.

•Chloroform is the dominant species (> 80%) in wastewater effluent.

•Compared to SABS and FEPA the levels of DBPs formed in both tap water and wastewater effluents were low. Therefore our water is safe for the environment and to human.

  1. References
  1. J.K Edward, Water Quality & Treatment A Handbook on Drinking Water, 6th Edition,2011, AWWA
  2. T.Ivahnenko, & J.S.Zogorsla, Source& Occurrence of Chloroform and other Trihalomethanes in Drinking Water Supply Wells in United States.
  3. Johannesburg Water. Operation,2001.
  4. Metcalf & Eddy, Wastewater Engineering Treatment and Reuse, 4th Edition, 2004, McGraw Hill
  5. SABS241. Drinking Water Specification. Edition 5. SABS
  6. S.Yeats, & G.Hua, Control of Trihalomethanes in Wastewater Treatment. Presented at Florida Water Resource Conference, 2009.