Effects of Bio-sand Filter on Improving the Bio-stability and Health Security of Drinking Water

Effects of Bio-sand Filter on Improving the Bio-stability and Health Security of Drinking Water

Fengbing Tang, Zhennan Shi, Simin Li

School of Urban Construction Hebei University of Engineering

Handan, China fbtang1004@http://wendang.chazidian.com

Abstract—Bio-stability and health security of drinking water have become basic requirements to protect human health. The conventional water purification process, which is composed of coagulation, sedimentation, filtration and disinfection, can not solve the problems of organic matters in the micro-polluted source water effectively. So the by-products generated in the chlorination disinfection increased the carcinogenic risks of drinking water. The higher concentrations of Fe, Mn and trace heavy metals in the water are also harmful to health. In this study, bio-sand filter was adopted to treat the micro-polluted source river water. UV254 was used as a controlling parameter to measure the organic matters, BDOC and TP were used as evaluation parameters to measure the bio-stability of water quality. Combined with the removal of Fe, Mn and trace heavy metals in the source water, the effects of bio-sand filter on improving the health security and bio-stability of drinking water were investigated. The results demonstrate that bio-sand filter has good removal of UV254, and the average removal is 37.13%. The average removal of Fe, Mn and trace lead and chromium are 74.75%, 76.55%, 74.07% and 68.82%, respectively. The bio-sand filter has good removal of BDOC and TP. The average removal of BDOC is 61.78%. The removal of TP ranges from 58.76% to 78.53%, and the average removal is 68.62%. Applying the bio-filtration process in the water purification process can remove the biodegradable natural organic matters and control the production of disinfection byproducts, as well as the re-growth of micro-organisms in the water distribution system. The bio-sand filter process can remove Fe, Mn and trace heavy metals from the micro-polluted source water effectively. The bio-sand filter has great significance to improve the bio-stability of water quality, to limit the re-growth of microorganisms in the water distribution system and to protect human health.

Keywords-bio-sand filter; micro-polluted source water; health security; bio-stability; drinking water

I. INTRODUCTION

With the development of society, the advance of bio-detection technology and statistical accumulation of epidemiological data, people have got a further understanding of the risks of pathogenic micro-organisms and the potential damage of carcinogenic organic compounds. People have paid more and more attentions to the health security of drinking water quality, especially the problems of chlorination disinfection by-products.

Foundation item: Project (07276713D) supported by the Key Project of Hebei Province Science & Technology of China.

978-1-4244-7739-5/10/$26.00 ©2010 IEEE

Chengyuan Su

School of Environment and Resource

Guangxi Normal University

Guilin, China

suchengyuan2008@http://wendang.chazidian.com

The conventional water purification process, which is composed of coagulation, sedimentation, filtration and disinfection, is more suitable for the cleaner source water. But it can not get a perfect treatment effects for the micro-polluted water. The conventional process can remove the insoluble and colloidal organic matters from the source water effectively, but the removal of dissolved organic matters is relatively lower [1]. When the source water contained humic acid, fulvic acid and other organic compounds, the halogenoalkanes will be generated after the chlorination disinfection process [2]. Organic pollutants can react with the chlorine, so carcinogens will be generated, such as trihalomethanes (THMs), haloacetic acids (HAAs), and so on. In the water, more than 500 kinds of chlorinated organic compounds have been detected in the chlorination disinfection process and some of them are carcinogens or suspected carcinogens. So the carcinogenic risks of drinking water are increased. Meanwhile, if the heavy metals enter into water bodies, it is possible that can affect human health either directly or indirectly through the food chain [3]. The bio-filtration process in the water purification process can remove the biodegradable parts of the natural organic matters and control the production of disinfection byproducts, as well as the re-growth of micro-organisms in the water distribution system[4]. At the same time, bio-filtration process can remove Fe, Mn and trace heavy metals from the polluted source water.

In this study, bio-sand filter was adopted to treat the micro-polluted source water of Fuyang River in Handan, which is a city of Hebei province, China. The removal of UVtrace chromium and lead, BDOC (biodegradable organic 245, Fe, Mn, carbon) and TP (total phosphorus) were investigated and the effects of bio-sand filter on improving the bio-stability and health security of water quality were analyzed in order to provide references for the further research and development for bio-stability and health security of drinking water.

II.

MATERIALS AND METHODS

A.Quality of raw water

Fuyang River water was used as raw water in the experiment. Before 1990s, Fuyang river water was the water source of the Handan second drinking water treatment plant. Affected by industrial pollution, sewage pollution and

agricultural non-point source pollution, contents of organic matters, heavy metals, Fe and Mn increased with varying degrees. Water pollution has brought great difficulties to the production of the plant, so the plant stopped its production. The quality of raw water during the experiment period is shown in Tab. 1.

B.Experimental apparatus and methods

The experimental apparatus of bio-sand filter is made of organic glass, and its schematic diagram is shown in Fig. 1. The height of the filter is 2000 mm the diameter is 100 mm, the height of the supporting layer is 300 mm, the height of the quartz sand filter media layer is 1000 mm. The filtration head is 500mm above the media layer. Sampling holes are set at the different height of media layer. And the backwashing air distribution pipe, backwashing water distribution pipe and the effluent pipe are set. The quartz sand, with the diameters of 3–5 mm, is used as filter media, the average diameter is 0.8mm, K80<2.0. In the middle water tank, compressed air pipe is set to aeration. Downflow filter is adopted. Under the normal operation conditions, the hydraulic loading is 3m/h. All the water-quality items were measured by Standard Methods.

III. RESULTS AND DISCUSSION

The structure and function of aquatic ecosystems and the utilization of micro-polluted source water has been seriously affected due to the water environment pollution by organic pollutants and trace heavy metals. Therefore, it is significant to analyze the effects of bio-sand filter on improving the bio-stability and health security of drinking water.

TABLE I. QUALITY OF RAW WATER

Items Concentration of pollutants

Temperature

NH4-N mg/L

CODMn mg/L

Turbidity NTU

TOC mg/L

Chroma degree

Figure 1. Schematic diagram of experimental apparatus

A.Removal of UV254 by bio-sand filter and its factors 1)Removal of UVThe micro-polluted source water usually contains trace 254 by bio-sand filter

natural organic matters (NOM) and synthetic organic compounds (SOC). These organics, which would produce trihalomethanes (THMs), haloacetic acids (HAAs) and other disinfection byproducts in the chlorination process, can not be removed effectively by the conventional water purification process. It also can promote the re-growth of microorganisms in the water distribution system. Therefore, it is very necessary to remove the precursors of disinfection by-products, which could be generated in the disinfection, before chlorination process [5]. The most great significance of UVtreatment is that it can be used as substitution parameter for 254 in water total organic carbon (TOC), dissolved organic carbon (DOC), precursors (THMFP) of chloroform (THMs), etc.. So it is an important controlling parameter of organic matters in water

treatment. The removal of UV Fuyang river water treatment was studied, and Fig. 2 shows the 254 by bio-sand filter for the

removal effects at the temperature of 18 -27 .

From Fig. 2, it can be seen that the bio-sand filter has good UV254 removal effect for the Fuyang river water. The removal ranges from 32.47% to 46.15%, and the average removal is 37.13%. The removal of UV254 by bio-sand filter process reduced the possibility of trihalomethanes, haloacetic acids and other disinfection by-products which could be generated in the chlorination process of the micro-polluted source water treatment. Therefore, bio-sand filter process improved the health security of drinking water effectively.

2)Influence factors of UV254 removal by bio-sand filter a)Influence of temperature

The decrease of temperature can lead to the decrease of microbial enzyme activities. So the oxidation and decomposition rates of the organic matters by microorganisms can be affected. When the temperature decreased, the water viscosity increased at the same time. Therefore, the substrates transfer rates are affected and the pollutants removal descended. The UV254 removal by bio-sand filter at different

temperatures is shown in Tab. 2.

b)Influence of hydraulic loading Hydraulic retention time (HRT) can be affected directly by

hydraulic loading. The lower hydraulic loading, the longer hydraulic retention time. When the hydraulic loading

increased, bio-activities are enhanced by the stronger washing

Figure 2. Removal of UV254 by bio-sand filter

of filter media. But with a further increase of hydraulic loading, the volumetric loading of the reactor will be increased, and HRT will be reduced to a large extent and the biological treatment effects will be affected. At the temperature of 18 -27 , the removal efficiency of UV254 by bio-sand filter under the different hydraulic loading is shown in Tab. 3.

B.Removal of Fe, Mn and heavy metals by bio-sand filter If the water contains high concentrations of Fe and Mn the certain damage can be caused. The heavy metals bio-degradable organic matters to support the growth of

heterotrophic bacterial in the water, namely the maximum possibility of the organic nutrients to support the growth of bacterial when the organic matters become to a limiting factor for the growth of heterotrophic bacteria in the water. The measurements of bio-stability of water quality are mainly including bio-assimilable organic carbon (AOC) and biodegradable organic carbon (BDOC). BDOC refers to the organics which present in the drinking water and can be degraded by bacteria or be synthesized into cell bodies. As a accumulated in the human body could endanger health. The hexavalent chromium (Cr6+), which is the main element to affect human health, is stable in the rich oxygen condition and can maintain a long period. Lead, which can enter into the digestive system of human body with water and food and can also enter into the respiratory system with air, is a harmful element to the health. It is reported that there is no accumulation effect for adults if the Pb intake is less than 0.32 mg per day, but there will be an obvious accumulation effect if its intake is more than 1mg per day.

Therefore, the removal of Fe, Mn, Cr6+ and lead by bio-sand filter during the experiment were studied at normal temperature. The results are shown in Tab. 4. From Tab.4, it indicates that the bio-sand filter has good removal of Fe, Mn and trace heavy metals in the micro-polluted Fuyang river water treatment. It is considered that the Fe removal by bio-sand filter is mainly due to the combination of contact oxidation and micro-organisms, the removal of Mn is mainly relies on catalytic oxidation of manganese-oxidizing bacteria, such as sphaerotilus, and the removal of trace heavy metals mainly relies on the combination of mechanical filtration, biological flocculation and bio-adsorption. It can obtain good coagulation and adsorption effects through microbial secretions and some chemical structure of organism and its composition characteristics. It has been found that some bacteria, algae and cell extracts have the function to adsorb the metal ions. With a stable biofilm layer on the surface of the sand media, bio-sand filter gets good removal of trace heavy metals, so that the security of the drinking water can be improved effectively. C.Removal of BDOC by bio-sand filter

Bio-stability of drinking water refers to the capability of the

TABLE II. REMOVAL OF UV254 AT DIFFERENT TEMPERATURES Temperature ( Average removal (%) 15.05 25.59 37.13 TABLE III. REMOVAL OF UV254 UNDER DIFFERENT HYDRAULIC LOADING

Hydraulic loading Average removal (%) 29.8 31.4 37.13 30.6 25.3 TABLE IV REMOVAL OF Fe, Mn AND TRACE Pb AND Cr Parameter Influent (mg/L) Effluent (mg/L) Removal rate (%)

Pbpartial of BDOC, AOC refers to the organics which can be converted into cell bodies and it can the most easily be absorbed by bacteria and be synthesized into cell bodies directly [6].The studies have shown that when the BDOC concentration in the effluent of drinking water treatment plant is higher than 0.234mg/L, the water can be regarded as biological instability. And there is an obvious correlation among the concentration of BDOC, biological stability of the water quality and the number of heterotrophic bacteria in the distribution system [7]. The removal of BDOC by bio-sand filter at normal temperature is shown in Fig. 3.

From Fig. 3, it can be seen that the bio-sand filter has good removal of BDOC. The minimum, maximum and average removal rates are 55.02%, 73.47% and 61.78%, respectively. BDOC contains the substance and energy source of heterotrophic bacteria's metabolism, so it can be used as evaluation parameter of total bio-degradable organic matters. The bio-sand filter improved the water quality and has great significance to limit the re-growth of microorganisms in the water distribution system and ensure health.

D.Removal of TP by bio-sand filter

As a key nutrient for microbial growth and multiply, phosphorus plays a critical role in the microbial reproduction and growth and has been paid widely attentions in the field of sewage treatment. In drinking water treatment process, the phosphorus concentration, to a large extent, is the more practical controlling factor to determine the re-growth of micro-organisms in the pipe networks and bio-stability of the water. Compared with the AOC and BDOC, the phosphorus concentration has more practical application value on the analysis and detection of treatment effects in water treatment process [8]. In addition, the detection of phosphorus is relatively simple than AOC and BDOC in the water treatment plant. So phosphorus can be used as the controlling parameter of the water bio-stability.

Figure 3. Removal of BDOC by bio-sand filter

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Figure 4. Removal of TP by bio-sand filter

Bio-sand filter was adopted to treat the micro-polluted Fuyang river water in this study, the removal of TP at the normal temperature is shown in Fig. 4.

From Fig. 4, it can be seen that the bio-sand filter has good removal of TP. The removal rate ranges from 58.76% to 78.53%, and the average removal is 68.62%. The concentration of phosphorus in the effluent can limit the re-growth and reproduction of the microorganisms in the distribution pipeline networks. The bio-sand filter process can improve the bio-stability of the drinking water, so it has great significance to health.

At present, to control the phosphorus in water bodies has been given a particular attention all over the world. The researchers Sathasivan, et al. [9] have found that the phosphorus can restrict the growth of bacteria in drinking water. With concentration of 1-3 g/L, the phosphorus may become a

limiting factor for the growth of microorganisms in drinking

water. Therefore, to study and develop the technologies and methods of the phosphorus removal in drinking water treatment

is directly related to the attainment of the goal that uses the phosphorus to control the bio-stability in the drinking water. If the research in this area obtained success, it will open up a new way to control the bio-stability of drinking water. There will be great significance to improve the health security of water quality [8]. The results of the study demonstrate that the bio-sand filter has achieved good phosphorus removal in micro-polluted source water treatment process. But it still needs a

further exploration to recognize the mechanism of phosphorus

removal in the bio-sand filter process. IV.

CONCLUSIONS

The health security and bio-stability of drinking water is critical to health. When the organics in the source water increased, the effluent of the conventional water purification process can not meet the standards requirements of drinking water quality. So the carcinogenic risks of drinking water are increased by the chlorination disinfection by-products. Applying the bio-filtration process in the water purification process can remove the biodegradable natural organic matters and control the production of disinfection byproducts, as well as the re-growth of micro-organisms in the water distribution

system. The results of the study demonstrate that bio-sand filter has achieved good effects in micro-polluted Fuyang river water treatment process.

1) The average removal rate of UV254 by bio-sand filter is 37.13%. So it reduced the possibility of trihalomethanes, haloacetic acids and other disinfection by-products. The security of drinking water is improved.

2) The bio-sand filter process has good removal of Fe, Mn and trace heavy metals. The average removal of Fe, Mn, Pb and Cr are 74.75%, 76.55%, 74.07% and 68.82%, respectively. The Fe removal is mainly due to the combination of contact oxidation and micro-organisms, the removal of Mn mainly relies on catalytic oxidation of manganese-oxidizing bacteria and the removal of trace heavy metals mainly relies on the combination of mechanical filtration, biological flocculation and bio-adsorption.

3) BDOC can be used as evaluation parameter to measure the bio-stability of water quality. The average removal of BDOC by bio-sand filter is 61.78%. So the bio-sand filter has great significance to improve the bio-stability of water quality, to limit the re-growth of microorganisms in the water distribution system and to protect people's health.

4) The phosphorus concentration is a more practical controlling factor to limit the re-growth of micro-organisms in the pipe networks and ensure the water bio-stability. So TP

can be used as the controlling parameter of bio-stability in the drinking water. The removal of TP by bio-sand filter ranges from 58.76% to 78.53%, and the average removal is 68.62%. REFERENCES [1] S. Rscoot, “Bench scale evaluation of GAC for NOM Control,” Journal

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