Treatment systems optimization for the sewage water.

Alexandrescu, Aurora

1. INTRODUCTION

Investigations on organic and inorganic water pollutants have had a significant impact on environmental sciences by providing reliable knowledge on inputs and environmental exposure in such a way that risk assessments can be performed. Especially important have been the development of chemical analytical techniques, which allow qualitative identifications and quantitative determinations of trace concentrations in aqueous and solid samples. A large number of environmental contaminants have been studied regarding their fate and behaviour in the environment, (Bate, 2006). The paper describes the influence filtration methods about water's quality. It is distinguished the capacity of some polymer mixtures of different types to react on a lot of quality parameters of water. It is presented a comparison between the retaining efficiency of the organic substances and organic carbon after clarifying step, respectively of filtration on quartz sand stratum. It is analysed the reduction efficiency of organic filling case usage of polymers mixture. The indicator's allowance depends of technology type used in the treatment process, (Chapra et. al., 1997).

The application's advanced coagulation requires process modifications for the water plants. These modifications can improve the disinfection at pH reduced, but can make big slush quantities. The experimental researches concerning the optimization of the coagulation--flocculation process allowance following problems:

1. The influence of the water quality on the reagent type of coagulation.

2. The regent type's influence concerning abeyances abstention efficiency and organic substances for different sources.

3. The improvement of the coagulation process with different coagulants (through polymers). The coagulation tests are effectuated in laboratory and pilot installations. The specific polymers for the drinkable water's treatment and the polymers obtained through irradiation with electrons and microwaves have been tested. Aluminium sulphate is used like polymer admixture.

4. The pH's influence on the coagulation process. The coagulation tests have used aluminium sulphate and ferric chloride.

The advanced coagulation represents the reduction process of the natural organic substances in the water's treatment channel. It is a correlation between the three-halo-methane and the total organic carbon concentration from brute water. The coagulation adjuvants are natural or synthesis substances used for the improvement of the coagulation process's performance, (getting of big flakes). The coagulation adjuvants doses may be established through coagulation--flocculation tests and tests on slush. The spell between the coagulant's injection and coagulation adjuvant's injection is very important. It is efficient as the polymers to be injected after what the micro-flocculation phase is fully. The water's composition and the temperature influence this spell. It is considered a particle j situated in the origin of co-ordinates system and liquid debit from a sphere of [R.sub.j] = [R.sub.i]+ [R.sub.j] radius. Speed gradient is equable. The collisions number [N.sub.i] with central particle j is, (for [n.sub.i] particles of i dimension on volume unity):

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. (1)

Equation (1) may be written depending on the particles diameter [d.sub.i] [d.sub.j] and the speed gradient dv / dz = [bar.G]. Smoluchowski equation for the kinetic stage supposes that each collisions carries at flakes formation; the particles are destabilized. If y is net electrostatics potential energy, then d[psi]/dr is electrostatics force that acts on particles, at r distance against j central particle. Equation (2) is bringing; the limit conditions are following: n = [n.sub.o] for r = [infinity] and n = 0 for r = 2R. It is obtained mathematical relation, ([D.sub.[infinity]] = [D.sub.i] + [D.sub.j]):

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. (2)

2. EXPERIMENTAL RESULTS

The experimental determinations are effectuated at Chirita Iasi water plant. The measures for the establishment of the optimum coagulation conditions are make obvious through experimentation. Maximum efficiency of coagulation's achievement is determined by the substances and concentrations used. The powder active coal is necessary to dose correct in the optimization process of the coagulation--flocculation, because of the pesticides presence in water. It is obtaining the biologically steady water. The water treatment with elevated content of sulphide hydrogen requires an oxidation process for the transformation in colloidal sulphur; it is removed the sulphur through clarifying process, (Liu et al., 2009). The experimentation is effectuated on ground water with ammonium and hydrogen sulphate content. The oxidation is realized through the usage of sodium hypochlorite. It is analysed the possibility of removal of the sulphides and the hydrogen sulphate through oxidation and filtration with quartz sand, respectively hyper filtration. It is following the improvement of the oxidised water's clarifying process through coagulation process. The coagulation process's efficiency grows through usage of flocculants; it is obtained slush volumes lesser, (Suthers & Rissik, 2009).

It is analysed the water's quality from Prut river in the Tutora section. It is found the following properties:

1. The water has big variations of turbulence and is feeble colored.

2. pH is in the alkalescent domain (8,06 / 8,16) pH units; the total alkalinity is (3 / 3,5) mechiv/l.

3. The mineralization indicators (fixed residue and conductivity) have values adequate to the mineralised average water; the mineralization is given by the bicarbonates and the calcium sulphates.

4. The concentration of organic substances is established with potassium permanganate in the interval (10 / 26) mg/l K Mn O4. The concentration of organic substances is established with potassium bi-chromium in the interval (12 / 15) mg/l O2. These values may conduct at difficulties in the water's treatment.

The pesticides concentration from water has excelled many times (5 / 10) times the accepted concentration for drinkable water, (Hatzinger et al., 2009). It is used a treatment channel with following processes:

1. Oxidation with Cl[O.sub.2] and ozone. Advanced coagulation with ferric chlorides (14,5 mg/l) and brute water acidifying with 2,5 % HCl solution, (18,5 mg/l).

2. Clarifying in clarifying tank with concentrated dynamical stratum at hydraulic attempts [i.sub.h] = 4 m/h. Castigation pH with lime water, (dozes of 28 mg/l).

3. Quick filtration on quartz sand stratum. The seeming filtration speed is [V.sub.f] = 6 m/h. Post--oxidation with ozone (1 mg O3/l) after quick filtration on sand. Filtration on granular active coal with seeming filtration speed [v.sub.f] =5 m/h and time t = 8 min. Final disinfection with sodium hypochlorite, (dozes chlorine 1 mg/l).

It is tested water sources with aluminium sulphate and ferrous chloride at (6 / 6,5) pH. It is ascertained the reduction of turbulence and organic substances' oxidation. The usage of the ferrous chloride reduces organic loading, particularly at oxidable hard organic substances. The coagulation--flocculation tests make obvious the water's aggressiveness growth through treatment. The castigations with lime water eliminate the aggressiveness effect of water. Also grow up the total organic carbon quantity with (30 / 40) %. After organic substance' removal may be corrected pH. It is necessary lime dozes between (8 / 10) mg CaO/l.

Figure 1 present the concentration's variation of total organic carbon depending on pH for lime water treatment from Chirita treatment station. The polymers conduct at different efficiency all over: turbulence and organic loading. It is used polymers mixtures for coagulation--flocculation treatment in laboratory. The best behaviour has been the mixture c. Polymer optimum dose is 0,2 mg/l, (figure 2). The experimentation in laboratory has used simple polymers and polymers mixtures. Some polymers mixtures have acted simultaneous about several quality parameters of water.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

3. CONCLUSIONS

The studies concerning the water's treatment in Chirita treatment station make obvious the following conclusions:

1. Te water source present treatment difficulties because of elevated concentration of organic substances; concentration of total organic carbon is (10 / 18) mg C/l. Removal maximum efficiency of the organic loading through advanced coagulation is obtained with ferric chloride (5 / 7) mg [Fe.sup.3+]/l and reduced pH (6 / 6,5). It is necessary to use powder active coal for the coagulation--flocculation optimum process. The water's treatment with ozone and granular active coal establish good qualities, in the limit imposed by the standard.

2. Sulphide hydrogen may be eliminated with 100 % efficiency using filtration and oxidation with chloride. The filtration process on sand has not good efficiency; it is not drinkable water. It is necessary the coagulation--flocculation and clarifying process. It is recommended the clarifying tank with (4 / 5) m/h and sedimentation time of 1 h. The nitrogen may be eliminated through treatment with chlorine. The filtered water on diaphragm has the standard qualities.

4. REFERENCES

Bate, R. (2006). All the Water in the World, Pb. The Centre for Independent Studies, ISBN 9781864321159

Chapra, S. C.; Canale, R. P. & Ami, G. L. (1997). Empirical models for disinfection by products in lakes and reservoirs, Journal of Environ Engineering, ASCE, 123 (7), pp. 714-715

Hatzinger, P. B.; Bohlke, J. K. & Sturchio, N. C. (2009). Fractionation of stable isotopes in perchlorate and nitrate during in situ biodegradation in a sandy aquifer, Journal Environmental Chemistry, Research Front Perchlorate in the Environment, CSIRO PUBLISHING, Volume 6, 44, Number 1/2009

Liu, C. S.; Zhang, L. J. & Feng, C. H. (2009). Relationship between oxidative degradation of 2-mercaptobenzothiazole and physicochemical properties of manganese (hydro)oxides, Journal Environmental Chemistry, Research Front Perchlorate in the Environment, CSIRO PUBLISHING, Volume 6, 83, Number 1/2009

Suthers, I. M. & Rissik, D. (2009). Plankton, A Guid to Their Ecology and Monitoring for Water Quality, CSIRO PUBLISHING, ISBN 9780643090583

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*** http://www.ecosmagazine.com (2009). Greywater gets standard treatment, ECOS 5, ISSN 0311-4546, 147/Feb- Mar/2009