Using Huwa-san as Alternative Disinfecting Agent for Water

Treatment

Presented by

Yaser Hagag Mohamed

Greater Cairo Drinking Water Company (CGWC)

Introduction

Chlorination is widely used in several countries to ensure a safe drinking water. The chlorine reacts with natural organic matter forming disinfection byproducts which have been related to the occurrence of cancer, growth retardation, spontaneous abortion, and congenital cardiac defects.

It is a non-selective oxidant, and therefore reacts with both organic and inorganic chemical species in water, as well as functioning as an antimicrobial agent.

Chlorine, added to water in the form of hypochlorous acid/hypochlorite ion or as chlorine gas, is still the most widely used and most cost-effective disinfectant worldwide.

The chlorine reacts with natural organic matter to form disinfection by products. The higher the organic load of chlorinated water, the more disinfection byproducts will be formed. However, the amount of disinfection byproducts generated not only depends on the concentration of natural organic matter but also on the total algae count. So many studies were directed to search for alternative safe disinfecting agents.

Huwa-San was produced as a disinfectant for biofilm removal. The previous study was restricted to evaluate with respect of Huwa-San capacity to remove the biofilm on pipe systems of drinking water. It is based on silver stabilised hydrogen peroxide.

The treatment with Huwa-San showed a strong decrease in density of the microorganisms. This required a higher dose rate of chemicals and it depends completely on important factors as the concentration of Huwa-San ; contact time and mode of treatment which may be static or in circulation.

It is highly effective against gram negative and gram positive, aerobic and anaerobic, spore forming and non spore forming pathogenic and saprophytic bacteria. It will not impart taste or taint or smell to water or any substrate to which it is applied and it is characterized that there is no by-products. So, the present experiment was directed to study Huwa-San as alternative disinfecting agent during water treatment.

Aim of the work

The current experiment aims to search for new disinfecting agent without formation of by-products to replace the chlorine. The study was carried out at all the levels.

Materials and Methods

Nile Sample

Nile water samples were taken from water intake throughout the fustat water treatment plant.

Jar test

This test was carried out using different concentrations of disinfecting agent at constant coagulating agent (30 ppm Al2(SO4)3).

Disinfecting agent

Nile water samples were dosed with disinfecting agent at six different concentrations including 2, 3, 4, 5, 6 and 7 ml. These concentrations were prepared from solution with concentration (1 % - 10 mg L-1).

The disinfecting agents which were under study

Chlorine

The chlorine residues were measured by the DPD colorimetric method.

Huwa-san

There was no free chlorine to be measured.

Measurements

Chemical measurements by titrimetric method Hardness

The total and calcium hardness were measured in water matrix by titration against EDTA depending on type of indicator.

Chlorides

Chloride in the water samples determined by using Argentometric method by titration against silver nitrate in presence of potassium chromate.

Alkalinity

Alkalinity is the acid neutralizing capacity. It used to determine alkalinity of carbonate, bicarbonate and hydroxyl content by titration against sulfuric acid in presence of methyl orange as indicator.

Chemical measurements by electrode

Dissolved Oxygen (D.O)

The DO gave indication to measure the oxygen needed for all oxidation,

nitrification and decomposition processes.

pH

The pH value gave indication to concentration of the hydrogen ions (H+) obtained as a result of dissociation or hydrolysis process.

Conductivity

The conductivity value gave indication to concentration of the minerals in the water matrix and hence ability of the aqueous solution to carry electric current.

Chemical measurements by photometric techniques

Turbidity

The turbidity value gave indication to small and large particles scattered throughout the matrix.

Sulfates

Sulphate concentration in the water samples were determined by Turbidimetric method after precipitation of sulphate ions as crystals of barium sulphate.

Heavy metals

Aluminium and iron were measured spectrophotometrically at specific wave lengths after certain processing.

Microbiological examination

The total coliform occurred and fecal coliform were detected total and fecal coliform membrane filter procedure.

The pour plate method occurred to compare the disinfecting effect of chlorine and huwa-san at the same doses on the microbial growth.

The total algae count (TAC) measured using counting cell. The low magnification method is the most suitable method for the plankton counting.

Results and Discussion

- There was free residual chlorine obtained as a result of water disinfection by chlorine. There was no residual chlorine in case of huwa-San.

- There was direct relation between the chlorine dose added during the treatment and concentration of the residual

Fig. : Chart showing values of residual chlorine after water disinfection by chlorination at the doses 2, 3, 4, 5, 6 and 7 ppm.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the dissolved oxygen

- The chlorination decreased D.O. while the huwa-san increased it in a dose dependent manner.

- The hydrogen peroxide molecule contains one extra oxygen atom, compared to the more stable water molecule. The bond between the two oxygen atoms, the so-called peroxide bond, is broken while two H-O radicals are formed.

- There is no simple correlation between adding chlorine and dissolved oxygen.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the conductivity value.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the pH value.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the turbidity value.

- The turbidity value showed that the disinfection by both of chlorination and huwa-san has the same effect on the turbidity value. This may refer to decreasing the total particle counts.

- The Turbidity in water is the reduction of transparency due to the presence of particulate matter such as clay or silt, finely divided organic matter, plankton or other microscopic organisms. These cause light to be scattered and absorbed rather than transmitted in straight lines through the sample.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the total hardness.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the magnesium hardness.

- The chlorination increased the total and calcium hardness due to maintaining the minerals soluble in the chloride forms and this caused increase in the total hardness. The disinfection by huwa-san has no obvious effect on the total and calcium hardness at any dose.

- The disinfection by the two ways changed Mg hardness in a dose independent manner. This because magnesium compounds are much more soluble than their calcium counterparts so the concentrations of magnesium are extremely high.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the chlorides.

- The chlorination increased the chlorides directly with increasing the chlorine dose in a dose dependent manner.

- The disinfection with huwa-san has no any effect on concentration of the chlorides. This may be due to involving of chlorine in formation of byproducts as chloroform which caused elevation of the chlorides.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the chlorides.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the Alkalinity.

- The chlorination at the doses 6 and 7 ppm decreased alkalinity obviously giving indication to normal role of chlorine in the treatment process while the disinfection with huwa-san maintained the alkalinity level due to the presence of hydroxyl group which contributed in maintaining the alkalinity level.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on Aluminium measured by spectrophotometric method.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on Iron measured by spectrophotometric method.

- It was found that the disinfection by chlorine and huwa-san caused decrease in Al and Fe in a dose independent manner. Both of chlorine and huwa-san caused deposition of Al and Fe as AlCl3, FeCl3,

Al(OH)3 and Fe(OH)3.

- The disinfection by chlorine at the doses 6 and 7 ppm showed more effect on Al than huwa-san. Huwa-san was more effective in decreasing iron concentration during treatment than chlorine. Rate of iron deposition in form of Fe(OH)3 was more rapid than that in form

of FeCl3.

Fig. : Chart showing comparison between chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the Total Algae Count.

Table : Effect of chlorination and huwa-san at the doses 2, 3, 4, 5, 6 and 7 ppm on the total and fecal coliform, plate count and total algae count.

- The microbiological data showed that both of chlorine and huwa-san have the same disinfecting effect at the same doses on all the parameters (total, fecal coliform, TAC and protozoa living in fresh water).

- Both of chlorine and huwa-san decreased the TAC obviously in a dose independent manner.

- The pour plate method confirmed that the chlorine is more effective than huwa-san against the bacterial growth. It was found that the chlorine inhibit the bacterial growth completely at any chlorine dose while the huwa-san at the dose 10 µl decreased the bacterial growth from 5000 to 2000 colony forming unit. The other huwa-san doses (15, 20, 25, 30 and 40 µl) have the same effect as chlorine.