nitrate treatment

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Development of physicochemical nitrogen removal processfor high strength industrial wastewater

Seungmoon Lee, Sanjeev Maken, Jung-Hwa Jang, Kwinam Park, Jin-Won ParkDepartment of Chemical Engineering, Yonsei University, 134 Shinchon-dong Seodaemun-ku, Seoul 120-749, Republic of Korea

a r t i c l e i n f o

Article history:Received 24 August 2005Received in revised form8 January 2006Accepted 12 January 2006

Keywords:DenitricationHigh strength industrial wastewaterPhysicochemical nitrogen processBiological nitrogen removal processSulfamic acidNitrate ion

A B S T R A C T

The biological nitrogen removal (BNR) process is the most common method for removing low quantities of ammonium from wastewater, but this method is not used for wastewaterrich with ammonium. In this study, we have developed the physicochemical nitrogenremoval process to remove the nitrogen content for a real industrial wastewater. Thedenitrication was accomplished by the physicochemical denitrication process using zincpowder and sulfamic acid in pH 2–4. The experimental parameters were examined byvarying various reaction conditions such as pH, zinc feeding time, amount of sulfamic acid,and amount of nitrate concentration. For each experimental condition, the physicochem-ical denitrication process was determined by pH, amount of zinc powder and sulfamicacid, zinc feeding time and nitrate concentration.

& 2006 Elsevier Ltd. All rights reserved.

1. Introduction

Nitrate contamination of water resources is becoming aserious environmental problem worldwide ( Carrera et al.,2004; Fan et al., 1996; Hu et al., 1999; Prosnansky et al., 2002 ;Sakakibara et al., 1994 ; Yu and Fang, 2003). High nitratelevels in water can cause methemoglobinemia, a conditionfound especially in infants of age under 6 months. Severe

methemoglobinemia can result in brain damage andeven death. Also, animals are affected by nitrates in thesame way as human babies ( Matsushita et al., 2001 ; Ono et al.,1996, 2000).

Advanced wastewater treatment processes for nitrogenremoval are usually separated into biological denitricationand chemical denitrication ( An et al., 1996; Fanning, 2000;Hasegawa et al., 2000 ; Itokawa et al., 2001 ; Liang et al., 2006;Zhang et al., 1998 ). The biological denitrication is separatedinto aerobic nitrication and anaerobic denitrication which

removes TN or TKN (NH3 –N/NH4+ –N, NO2 –N, NO3 –N) (Fu et al.,

2001, 2002; Kim et al., 2002; Park et al., 2001; Wen et al., 1998 ).This process is a two-step process ( Lee et al., 1999; Nam et al.,1998; Poo et al., 2005). In the rst step, ammonia is convertedaerobically to nitrate (NO 3 ). In the second step, nitrates areconverted to nitrogen gas. The most important advantages of biological denitrication process are high potential removalefciency, relatively easy process control, and high process

stability and reliability ( Tchobanoglous et al., 2003 ). However,it was reported recently that nitrous oxide (N 2 O), one of theimportant greenhouse gases, could be produced during bothnitrication and denitrication in activated sludge andreleased to the atmosphere. Also, in the biological treatmentof high strength industrial wastewater, high concentrations of ammonium or nitrite inhibit the nitrication ( Anthonisen etal., 1976). The purpose of these treatment processes is toremove nitrogen from the sewage. Therefore, these methodsare not good to treat high strength industrial wastewaters.

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0043-1354/$ - see front matter &

2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2006.01.018

Corresponding author. Tel.: +822 364 1807; fax: +822 312 6401.E-mail address: [email protected] (J.-W. Park).

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The chemical denitrication process used for nitrogenremoval is air stripping, breakpoint chlorination, and selec-tive ion exchange. Air stripping of ammonia nitrogen can beremoved from wastewater by volatilization of gaseousammonia. The process is simple in concept, but high cost isits serious drawbacks. It is very expensive to operate andmaintain. The most important advantage of breakpointchlorination process is that, with proper control, all theammonia nitrogen in the wastewater can be oxidized ( Harp,2003). Ion exchange using zeolites is technologically simpleand enables efcient removal of even traces of impuritiesfrom solution or substances. Zeolites can be effective inremoval of ammonia from wastewater ( Sarioglu, 2005; Meteset al., 2004; Bowman, 2003). However, high concentration of cations will reduce ammonia removal capability and pre-treatment by ltration is usually required to prevent thebuildup of excessive headless due to suspended-solidsaccumulation.

Chen et al. (2003) studied the removal of nitrogen using membrane bioreactor from opto-electronic industrial waste-water which contains a signicant quantity of organic carbonand organic nitrogen compounds with a ratio of over 95% inorganic nitrogen to total nitrogen and achieved an excellentremoval of 94% and 92% for COD and total Kjeldahl nitrogen.An aerobic rotating biological contactor was developed anduse for a simultaneous carbon removal, nitrication anddenitrication under aerobic conditions from two concentra-tions of high strength synthetic wastewater along with over90% COD removal and 60% nitrication ( Gupta and Gupta,2001). Krzemieniewski and Rodziewicz (2005) reported thelowest efciency (44.5%) of the denitrication without currentpassage in a rotating electro-biological contactor (REBC)which was found to be increase with current density toover 64.3%.

On the other hand, physicochemical denitrication is asimple and robust chemical process that converts nitrate inwater into environmentally benign gaseous nitrogen. In thisprocess, nitrate-contaminated water is added to a simplechemical reactor, where it is contacted with two inexpensivechemical reagents —sulfamic acid and zinc. The most im-portant advantage of this process is low cost, is not limited bylevels of nitrate concentration, and is not sensitive to othercontaminants. Thus it may be applied to high strengthindustrial wastewater from the industries such as opto-electronic industry, fertilizer or pharmaceutical industry orfood industries dairy wastewater. Several other activities alsogenerate high-strength ammonium wastewater including human waste and agricultural waste.

Consequently, this study is focused on the efciency of thedenitrication of NO 3 –N using sulfamic acid and zinc powderin the acidic condition.

2. Experimental

2.1. Materials

The KNO3 was used as a source of ammonia in wastewater forthe experiment of denitrication process. Sulfamic acid

(99.8%) was used as a reducing agent of nitrous ion. The pHwas controlled by sulphuric acid (95%) and sodium hydroxide(98%). Sulphuric acid solution (0.1 N), boric acid (98%), K 2 SO4

(99%), CuSO4 5H2 O (99%), methyl red (pH: 4.2–6.2), bromcresolgreen (pH 3.8–5.4) and Devarda’s alloy (50Cu, 45Al, 5Zn) wasused for analysis of ammonia nitrogen and nitrate nitrogen.

2.2. Methods

The schematic of the reactor used for nitrogen removal fromhigh strength wastewater using zinc powder and sulfamicacid in pH 2–3.5 is shown in Fig. 1. The reactor was composedof four bafes to improve agitation. The capacity of reactorwas 7 l and zinc powder injector was installed in the upperpart of the reactor. Injected zinc powder was dispersed byagitator using pump. Zinc injector, pH meter were installed inthe reactor.

KNO3 and nitrogen concentration was analyzed by KjeltecAuto 2300 analyzer (Foss, Korea). To analyze nitrate nitrogenusing analyzer, the Devarda’s alloy was added in sample and

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Fig. 1 – Schematic diagram of batch reactor; 1 —Inlet; 2 —pHmeter; 3 —Zn powder inlet; 4 —Gas Vent; 5 —Screwcap; 6 —Outlet; 7 —Bafe; 8 —Impellor.

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titrated against nitrate nitrogen by colorimetric titrationmethod ( Fanning, 2000 ). MgO was added in sample during the analysis of ammonia nitrogen. The pH was measured byHamilton pH meter. The concentration of Zn 2+ ion spannedby dissolution of zinc powder was measured by inductivelycoupled plasma atomic emission spectrophotometer (IC-P–AES).

The reduction of nitrogen ion using zinc powder andsulfamic acid was examined under various reaction condi-tions, such as pH (2–3.5), amount of sulfamic acid(3880–6208ppm), amount of nitrate concentration(300–1000 ppm), and amount of zinc powder (2615–5230ppm).

3. Results and discussion

3.1. Effect of varying pH on nitrate ion removal

Ammonia conversion rate of nitrate ion removal with pH is

shown in Fig. 2. Ammonia conversion rate is low at the low

concentration of NO 3 –N (560ppm) and high at the highconcentration of NO 3 –N (1000 ppm). Ammonia conversionrate in high concentration of NO 3 –N was about 8–25%, andconversion rate in low concentration of NO 3 –N was about6–15%. It is thought that a low ammonia conversion rate inoverall nitrogen removal is protable in terms of economicalefciency with a decrease of breakpoint chlorination (BPC)cost.

3.2. Effect of the zinc concentration on nitrate ion removal

The reduction rate of nitrate ion for different concentrationof Zn according to the reaction time is shown in Fig. 3.The removal rate of nitrate ion is increase with increasein Zn concentration and is the maximum when the Znconcentration is 5230 ppm. The reaction almost completesafter 40min of reaction time. Ammonia conversionrate in high concentration of NO 3 –N was about 12–17%,and conversion rate in low concentration of NO 3 –N was about

5–12%.

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Fig. 2 – Normalize ratio of nitrate removal and ammonia conversion with variation in pH: (a) NO 3 –N (1000ppm), Zn(4707 ppm), sulfamic acid (5432ppm); (b) NO 3 –N (560ppm), Zn (4707 ppm), sulfamic acid (560ppm).

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3.3. Effect of sulfamic acid on nitrate ion removal

Concentration change of nitrate ion with reaction time fordifferent amount of sulfamic acid is shown Fig. 4. In case of 1000ppm NO 3 –N (Fig. 4(a)), the concentration reduction rateof nitrate ion also increased with the increase in amount of sulfamic acid. But, amount of sulfamic acid showed norelation in the reduction rate of nitrate ion in 560 ppmNO3 –N as shown in Fig. 4(b). In case of 1000ppm NO 3 –N,amount of 100–160% sulfamic acid was shown maximumconversion rate of ammonia was lower than 20%, andconversion rate of nitrate ion increased with increase of sulfamic acid. It is thought that reduction rate of nitrate ionas well as production rate of ammonia as a side-reactionincreased with the increase of sulfamic acid, and conversionrate of ammonia also increased. But, amount of sulfamic acidin 560ppm NO 3 –N showed no relation to conversion rate of ammonia.

3.4. Effect of nitrate concentration on nitrate ion removal

Effect of nitrate concentration on nitrate ion removal isshown Fig. 5. Reduction rate of nitrate ion increased with

increase in nitrate concentration. Also, ammonia conversionrate increase with reduction of nitrate ion. In results,ammonia conversion rate of 300ppm NO 3 –N and 1000ppmNO3 –N is high but ammonia conversion rate of 560ppmNO3 –N is low.

4. Summary

Characteristics of the denitrication of high strengthwastewater were studied. And found the denitrication of nitrogen depends on the Zn concentration, pH, andsulfamic acid and nitrate concentration. The efciencyof denitrication is protable in a low ammonia con-version rate (in 560 ppm NO 3 –N). The removal rate of nitrate ion is increase with increase in Zn concen-tration. The amount of sulfamic acid has no relationto conversion rate of ammonia. When nitrate concen-tration increased, reduction rate of nitrate ion alsoincreased.

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Fig. 3 – Normalized nitrate removal ratio and ammonia conversion ratio with varying amount of Zn powder: (a) NO 3 –N(1000ppm), pH (2.5), sulfamic acid (5432 ppm); (b) NO 3 –N (560 ppm), pH (3.0), sulfamic acid (5432ppm).

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Fig. 4 – Normalized ratio of nitrate removal and ammonia conversion with variation of the amount of sulfamic acid: (a) NO 3 –N(1000ppm), Zn (4707 ppm), pH (3.0); (b) NO 3 –N (560 ppm), Zn (4707 ppm), pH (3.0).

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Fig. 5 – Normalized ratio of nitrate removal and ammonia conversion according to the nitrate concentration: Zn (4707 ppm),sulfamic acid (5432ppm), pH (3.0).

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