GB2369115A

GB2369115A - Simultaneous removal process of nitrogen and phosphorus in wastewater

Info

Publication number: GB2369115A
Application number: GB0111584A
Authority: GB
Inventors: In Soo Kim; Sang Eun Oh; Yung Bok Yoo
Original assignee: Gwangju Institute of Science and Technology
Current assignee: Gwangju Institute of Science and Technology
Priority date: 2000-11-17
Filing date: 2001-05-11
Publication date: 2002-05-22
Anticipated expiration: 2021-05-11
Also published as: KR20020038322A; GB0111584D0; CN1354143A; GB2369115B; JP2002166293A

Abstract

This invention relates to a simultaneous removal process of nitrogen and phosphorous in wastewater, wherein it comprises: <SL> <LI>1) performing a simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic denitrification through supply of external carbon source in small amount (1/3-1/2 of requirement for heterotrophic denitrification) in full consideration of that facultative chemolithoautotroph, which is well growing in organic materials, among chemolithoautotrophic-based denitrification microorganisms; <LI>2) using a shell or a steel slag, together with sulfur particles, wherein (1) sulfur particles are used as electron donor and solid media on which sulfur denitrifier can grow, (2) as solid media, the shell plays a role to maintain pH 7-8 through the supplement of alkalinity when pH is further lowered due to hydrogen ion generated from sulfur denitification, while retaining the activity of denitrifying microorganism and supplying inorganic carbon source (CO<SB>2</SB>) for chemolithoautotrophs; and, <LI>3) performing a simultaneous removal process of phosphorous by precipitation in the presence of calcium ion (Ca<SP>2+</SP>) in water generated from shell or steel slag. </SL>

Description

SIMULTANEOUS REMOVAL PROCESS OF NITROGEN AND PHOSPHOROUS IN WASTEWATER This invention relates to a simultaneous removal process of nitrogen and phosphorous in wastewater, wherein it comprises : 1) performing a simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic denitrification through supply of external carbon source in small amount (1/3-1/2 of requirement for heterotrophic denitrification) in full consideration of that facultative

chemolithoautotroph, which is well growing in organic materials, among C > ZZ) chemolithoautotrophic-based denitrification microorganisms; 2) using a shell or a steel slag/sludge together with sulfur particles, wherein (1) sulfur particles are used as electron donor and solid media on which sulfur denitrifier can grow, (2) as solid media, the shell or steel slag/sludge plays a role to maintain pH 7-8 through the supplement of alkalinity when pH is further lowered due to hydrogen ion generated from sulfur denitrification, while retaining the activity of denitrifying microorganism and supplying inorganic carbon source (cl2) for chemolithoautotrophs ; and, 3) performing a simultaneous removal process of phosphorous by precipitation in the presence of calcium ion (Ca2+) in water generated from shell or steel slag/sludge Biological denitrification has been used successfully to remove nitrogen from wastewater. Usually, either autotrophic or heterotrophic denitrification system is used for this purpose. Heterotrophic denitrification is very efficient to remove nitrate by providing adequate amounts of organic carbon, and it is divided into two methods by the location of anoxic tank : pre-denitrification and post-denitrification. Such pre-denitrification is a cost-saving method using the organic materials in wastewater without adding external carbon source when organic carbon in the wastewater is sufficient compared to nitrogen, and its structure is composed of an ai-aerobic tank, anoxic tank followed by oxidation tank (aerobic tank) and.

precipitation tank in sequence. From the anoxic tank, denitrification reaction and organic decomposition are mainly being undertaken, while organic decomposition and nitrification occur in the oxidation tank. The nitrated wastewater in the oxidation tank is again returned to the anoxic tank for denitrification.

According to the heterotrophic post-denitrification method, it is difficult to control the addition of a high-priced external carbon source accurately enough to achieve complete removal of both nitrate (electron acceptor) and external carbon source (electron donor); furthermore, nitrogen-monitoring device also needs to be established, together with another automatic system of adding external carbon source accurately enough to remove both nitrate and a external organic carbon. If such external carbon source is added over that required for the heterotrophic process, the re-treatment process for external carbon source present in effluents needs to be performed.

The heterotrophic denitrification is a reaction performed by heterotrophic microorganism that serves to reduce nitrate or nitrite nitrogen into nitrogen gas using organic materials as electron donor under anoxic conditions. However, since the organic carbon concentration of various industrial wastewater generated from nitrogen/phosphorous fertilizer manufacturing, plied timber manufacturing, insecticide manufacturing and leather manufacturing as well as seepage water in filled-up land is relatively low compared to nitrogen, the heterotrophic post-denitrification. needs to use some high-priced organic materials such as methanol or acetate to reduce nitrate. In the case of treating a large amount of wastewater, the treatment cost for organic materials is enormously required.

To comply with this matter, many researches have focused on the sulfur utilizing chemolithoautotrophic denitrification method. In spite of significant denitrification efficiency in terms of economic aspect and stable treatment process, however, such method has recognized disadvantages in that the disruption of alkalinity due to hydrogen ion generated during denitrification results in lowering pH.

When 1goof nitrogen is reduced, 5mg of calcium carbonate (CaCO3) is consumed during chemolithoautotrophic denitrification. The optimum pH for most strains of denitrifiying bacteria has been reported to be between 7-8. In this respect the supply

of alkalinity is quite important so as to maintain pH in the neutral range (7-8). The conventional method has disclosed that alkalinity can be supplied using limestone in a tank, together with sulfur. In the case of wastewater containing a very high concentration of nitrogen such as seepage water, factory wastewater and livestock wastewater, however, the use of limestone only cannot provide a sufficient alkalinity due to limited rate of CaCO3 dissolution.

The sulfur-utilizing autotrophic treatment of high concentrations of nitrate results in high concentrations of sulfate production as by-products. So far, there is no official guideline available for discharge water in Korea to regulate sulfate ion, but it is defined as an esthetic material in the testing method for drinking water. The testing method for drinking water quality in Korea has prescribe that the contents of sulfate ion does not exceed 200 ppm, while WHO has defined it as 400 ppm. It has been reported that the high concentration of sulfate ion in drinking water may induce a sweet taste, but its extremely high concentration may corrode a conduit.

Since a sufficient amount of sulfate ion is present in natural water such as seawater (average 2,700 mg/L), the amount of sulfate ion in discharge waster produced from the system may be disregarded, unless wastewater having very high nitrate concentrations is treated. If sulfate ion in high concentration, during the treatment for nitrate nitrogen in high concentration, is discharged to a contaminated river, bad odor may be produced due to hydrogen sulfide (H2S). Thus it is preferred to prevent the formation of sulfate ion. Furthermore, since chemolithoautotrophic denitrification microorganism has a small growth yield (Y) value, its initial acclimation is quite difficult with a prolonged time required. Furthermore, since the surface of sulfur particle consists of hard and spherical form without porosity, a smaller binding site of microorganism may result in lowering the initial denitrification efficiency unless a large quantity of autotrophic microorganism is added to the reactor.

Currently, the quality standards for the discharge of wastewater have been strictly regulated in terms of the contents of nitrogen and phosphorous. Since the Korean government is schduled to prescribe the level of T-N and T-P in the wastewater treatment facilities by 20mg/L and 2mg/L, respectively, from the year 2002, it is safely said that the proper treatment for nitrogen and phosphorous is

inevitable.

In general, the biologically available method for the simultaneous removal of nitrogen and phosphorous include A2/0, modified Bardenpho method, UCT 0 p (University of Cape Town) method and VIP (Virginia Initiative Plant) method. However, since the aforementioned methods are entirely dependent upon heterotrophic denitrification microorganism, their actual application has not been widely made to wastewater containing a low C/N ratio. Among the conventional wastewater treatment methods for the removal of phosphorous only, chemical precipitation has been mainly used but its chemical cost is high with much occurrence of sludge.

To free from the aforementioned drawbacks such as disruption of alkalinity, formation of sulfate (S042-) and difficult acclimation of microorganism during the initial operation, the inventor et al. have made intensive researches. The Korean Patent No. 2000-60398, which was previously filed by the inventor, has disclosed better chemolithoautotrophic denitrification method using sulfur than heterotrophic denitrification method in that more stabilized treatment efficiency against temporary impact load can be achieved with economically advantage requiring no external carbon source This invention is an improved invention of the Korean Patent No.

2000-60398 filed by the inventor, which is intended for modifying the conventional sulfur-containing denitrification tank. More specifically, this invention is aimed for performing a simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic denitrification through supply of external carbon source in small amount (1/3-1/2 of heterotrophic requirement for denitrification), while supplementing some alkalinity by shell or steel slag and performing a simultaneous removal process of phosphorous by chemical precipitation in the presence of calcium ion (Ca2+) in water generated from shell or steel slag. Thus this invention has been completed.

Therefore, the purpose of this invention is to provide a denitrification method

so as to perform a simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic denitrification through supply of external carbon source in small amount (1/3-1/2 of heterotrophic requirement for denitrification).

Another object of this invention is to provide a method of supplementing the insufficient alkalinity during sulfur denitrification with the addition of shell or steel slag and of performing a simultaneous removal of phosphorous.

Fig. la is a sectional view showing an upstream tank for simultaneous removal process of nitrous nitrogen and phosphorous according to this invention.

Fig. lb is a sectional view showing a downstream tank for simultaneous removal process of nitrous nitrogen and phosphorous according to this invention.

Fig. 2 is a graph showing the denitrification efficiency of both heterotrophic and chemolithoautotrophic depending upon the amount of methanol addition.

Fig. 3 is a graph showing the denitrification efficiency of both heterotrophic and chemolithoautotrophic depending upon the amount of ethanol addition.

Fig. 4 is a graph showing the formation of sulfate ion depending upon the addition of methanol and ethanol.

Fig. 5 is a graph showing the changes of pH of burnt and dried shells with the lapse of time.

Explanation of Major Codes in the Drawings

1 : Sulfur and shell (or steel slag) 2 : Back washing 3 : Sulfur-containing denitrification tank 4 : Sand filtering tank 5 : External carbon source (methanol. ethanol, acetate, etc.

6: Pump 10: Upstream tank 20: Downstream tank This invention is characterized by a simultaneous removal process of nitrogen

and phosphorous in wastewater, wherein the wastewater treatment is performed in such a manner that sulfur particles and external carbon source in small amount (1/3-1/2 of heterotrophic requirement for denitrification) are added to a sulfur-containing denitrification tank so as to perform a simultaneous denitrification process for obligate chemolithoautotrophic, facultative chemolithoautotrophic and heterotrophic denitrification, while supplementing the depletion of alkalinity and removing phosphorous through simultaneous addition of shell or steel slag.

This invention is explained in more detail as set forth hereunder.

This invention relates to a post-denitrification method in which an anoxic tank is placed behind a nitrification tank. Sulfur may be used in the sulfur-containing denitrification tank as an electron donor and a carrier. Shell or steel slag also is added to the tank in a certain ratio for the alkalinity source. Additionally, the simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic is performed through supply of external carbon source in small amount (1/3-1/2 of heterotrophic requirement for denitrification) to influent.

With regard to microbiology, bacteria capable of oxidizing reduced sulfur compounds like sulfide, sulfur, or thiosulfate can be classified physiologically into four types: obligate chemolithoautotrophs, facultative chemolithoautotrophs, chemolithoheterotrophs, and heterotrophs. Obligate chemolithoautotrophs capable of denitrification, like Thiobacillus denitrificans and Thiomicrospira denitificans, are virtually restricted to an autotrophic mode of growth, since they cannot obtain energy from the oxidation of organic compounds, being able to utilize organic compounds

only to a limited extent. In contrast, facultative chemolithoautotrophic denitrificers, such as Thiobacillus verslltlls, Thiobacillus thynsiris, Thiosphaera pantotrophn, and Pamcoccits denit-ri 0 Przrncocclls denitrificans are not only able to grow autotrophically, by using reduced sulfur compounds as an energy source, but are also capable of heterotrophic growth. Hence, these bacteria can apparently adapt to different environments (i. e., autotrophic, heterotrophic, or mixotrophic conditions).

Table 1: Definition of the physiological types of bacteria able to oxidize reduced

sulfur compounds

Carbon source Energy source Category Inorganic Organic Inorganic Organic Obligate + - ~ chemolithoautotropha Facultative chemolithoautotrophB Chemolithoheterotroph - + + Heterotroph-+ + Synonyms : A obligate autotrophs ; B facultative autotrophs, mixotrophs As shown in the following scheme 1, the chemolithoautotrophic microorganism using sulfur serves to oxidize various sulfur compounds (S2-, S, S20s S406-, SO32-) into sulfate (SO42-), while simultaneously converting nitrate nitrogen to nitrogen gas.

Scheme 1 NO3- + 1. 10 S + 0.40 C02 + 0.76 H20 + 0.08 NH4 + # 0.5 N2 # + 1. 10 SO42- + 1. 28 H+ + 0. 08 CH7O2N Therefore, sulfur may be used in the sulfur-containing denitrification tank as an electron donor and a carrier.

In addition, some partial denitrification process in a reactor may be performed by heterotrophic denitrification microorganism, and facultative chemolithoautotrophic microorganism, since there are small amounts of external organic materials added in influent.

As shown in scheme 1, sulfur is oxidized into sulfate through the reaction between sulfur and nitrogen in influent, while nitrogen is simultaneously reduced into nitrogen gas for removal. However, under the circumstances where hydrogen ion is formed from the above reaction, the supply of alkalinity is extremely important in

providing pH conditions (pH 7-8) for denitrification To this end, shell is added to the tank, thus neutralizing hydrogen ion, as shown in the following scheme 2.

Scheme 2 CaCO3 + H+ Ca2+ + HCO3 Calcium ion (Ca2+), so formed from scheme 2, is reacted with phosphorous in influent to produce water-insoluble hydroxyapatite (Cas (OH) (PO4) 3)), as shown in the following scheme 3, thus removing phosphorous.

The typical materials used for removing phosphorous include rock phosphate, bone charcoal, artificial dephosphorization material derived from limestone, slug, etc.

The important selection criteria for dephosphorization materials include appearance, removal efficiency and economical advantage of solid form to be used.

Scheme 3 5Ca2+ + 3PO42-+ OH-~ Cas (OH) (PO4) 3, pKso = +55.9 Since the precipitation reaction of scheme 3 has a large pKso value, reaction may easily occur. The factors affecting precipitation include pH, concentration of calcium ion (Ca2+) and concentration of co-existent ion, including dephosphorization materials.

As shown in the following table 2, steel slag contains calcium oxide (CaO) as an active ingredient. Calcium oxide has been used as a neutralizer of acidic wastewater in the general wastewater treatment process. Table 2: Chemical composition of steel slag

Ingredient Percentage CaO 40-52 Si02 10-19 FeO 10-40

MnO 5-8 MgO 5-10 AbO3 1-3 P205 0.5-1 S < 0.1 Metallic Fe 0. 5-10 As noted in table 1, the objective of this invention can be achieved in such a manner that a simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic denitrification is performed through supply of external carbon source in small amount by taking advantage of the characteristics of facultative chemolithoautotrophic denitrification microorganism.

This invention is explained in detail based upon the accompanying drawings.

Figs. la and lb are schematic views showing a denitrification tank upstream 10, downstream 20] containing sulfur and shell for the treatment of nitrate nitrogen-containing wastewater (wastewater containing a low ratio of C/N), an

external carbon source (methanol, ethanol, acetate, etc.) and a sand-filtering device for ZD removal of biomass.

Influent suitable for denitrification include wastewater containing nitrate nitrogen with a low ratio of C/N, wastewater containing nitrate nitrogen after nitrification process, or waste water containing nitrogen in high concentration (seepage, livestock waste water, factory wastewater, etc.).

Sulfur particles and shell are added to the upstream and downstream tanks.

These sulfur particles may be used both as solid media on which autotrophs grow in a thin film and as an electron donor.

Since the growth yield (Y) value for obligate chemolithoautotrophic denitrification microorganism and facultative chemolithoautotrophic denitrification microorganism is small in the absence of carbon source in influent, a prolonged time is required for their initial acclimation time. To comply with this drawback, this invention has been completed with the following advantages:

1) The use of external carbon source in small amount (1/3-1/2 of methanol applicable in the general post-denitrification method) may ensure an easy acclimation of sulfur-containing denitrification tank, since facultative chemolithoautotrophic microorganism using organics is rapidly grown within the shortest time. According to the general heterotrophic post-denitrification method, 3 mg of methanol is added

for removing lmg of nitrogen ; 2) The tank retains a large number of microorganisms with a partial occurrence of heterotrophic denitrification; and the use of external carbon source in small amount may effectively prevent the discharge of organic materials, since organic materials are completely reacted in the tank; 3) To prevent the disruption of alkalinity during chemolithoautotrophic denitrification using sulfur, partial hydrogen ions formed from chemolithoautotrophic denitrification in the tank are neutralized by hydroxide ions formed in the heterotrophic reaction, thus minimizing the disruption of alkalinity; 4) To prevent the lowering of pH due to formation of hydrogen ion during the reduction of nitrous nitrogen by sulfur microorganism, the use of shell or steel slag serves to maintain the level of pH at 6-8 in order that denitrification microorganisms may exert their denitrification activity. It is preferred that sulfur and shell are mixed in the ratio of 4: 1-2: 1, and their addition needs to be made in consideration of inflow- concentration of nitrous nitrogen and supply period of shell; 5) Calcium ion (Ca2+), so formed from ionization of shell or steel slag, is reacted with phosphorous in influent to form water-insoluble (Cas (OH) (PO4) 3), thus removing phosphorous. The long-term operation of tank may cause some clogging due to floating materials of microorganism, thus requiring frequent back washing (2); and 6) Since the growth yield (Y) of sulfur denitrification microorganism is low, the concentration of microorganism in influent passed through sulfur-containing denitrification tank (3) is extremely low, thus removing microorganism in sand-filtering tank (4).

The. following specific examples are intended to be illustrative to the invention and should be construed as limiting the scope of the invention as defined by appended claims.

Example 1 1. 1) Experimental device and analysis summary To investigate the profiles of organic materials from sulfur microorganism-based denitrification in the presence of nitrate nitrogen in high concentration, a sulfur particle-containing column was operated by changing the concentration of organic materials under the conditions that alkalinity was less than theoretical amount for hetetotrophic denitrification.

Table 3: Experimental condition for column tests

Column Filler Organic Electron donor Conditions No. material E 1 Control-Sulfur NO3-N : 600mg/L plot Sulfur Low alkalinity (253g) Sulfur and Column 1 Methanol Room methanol E 2 temperature Column 2 Ethanol Sulfur and (24-25OC) Su particle size: 2-4mm HRT : 14 hours The reactors were inoculated using the aerobic return sludge from the municipal sewage treatment plant. After a contact time of 24 hours, the columns were operated continuously in an upflow mode for 20 days at a hydraulic retention time of 20 h (Table 1) to develop microorganisms on the solid media.

A black woven was used to prevent any influence of phototrophic microorganism using sulfur. The artificial inflow wastewater was composed of 600 mg N/ of KNOs, 1 g/t) of NH4CI, 2 g/L of KH2PO4, 0. 8 g/ of MgS04-7H20, 2 g/ {of NaHCOs and a trace of metal solution, plus methanol and ethanol. The wastewater treatment process was performed using influent alkalinity concentrations of about 930 mg/L as CaCO3, which was insufficient to remove NO3--N wholly (the theoretical necessary alkalinity is 3200 mg/L as CaCO). The column experiment

was also performed at room temperature.

Experiment 1 and Experiment 2 were intended to compare chemolithoautotrophic-based denitrification using only sulfur and some mixotrophic-based microorganism using methanol and ethanol as external carbon source.

In the case of Experiment 1 designed to induce sulfur microorganism-based denitrification, essential nutrients, buffer solution and nitrate nitrogen (600 mg of NO3--N/L) for treatment use were added to the column under an insufficient alkalinity in the absence of organic materials.

By contrast, to investigate the correlation among organic materials, sulfur particles contained in the column and treatment efficiency of microorganism, Experiment 2 was performed in such a manner that both methanol (T=1140 mg CH30H/L) and ethanol (T=822 mg C2H5OH/L) ranging from 1/4 to 1/2 of theoretical amounts were added to influent (600 mg of NO3--N/L) in the column as a basis of theoretical amounts of methanol/ethanol required for heterotrophic denitrification.

T refers to stoichiometric amounts for heterotrophic denitrification corresponding to 1.9 and 1.37 mg of methanol and ethanol, respectively, required per mg of nitrate-nitrogen removed. Schemes 4, and 5 were not considered the bacterial growth whose quantity is an additional amount of about 30% over the stoichiometric amounts given in below equations.

Scheme 4 6NO3-+ 5CH30H- > 3N2 + 5CO2 + 7H20 +60H- (methanol) Scheme 5 12NO3-+ 5C2HsOH- > 6N2 + 10C02 + 9H20 +120H- (ethanol) Hydraulic retention time (HRT) was fixed at 14 hours during wastewater treatment.. This corresponded to 1. 2 kg NO3--N/m3-d as a loading rate of NO3--N, being sufficient to remove NO3--N by more than 95% under a sufficient alkalinity according to the previous research.

When there were treatment results within 5% of analytical value, the analysis was performed by collecting influent and final effluent. The actual wastewater was p 0 used for the experiment of removing phosphorous. In the similar manner as above, the experiment was performed using the mixture of sulfur particles and shell in the ratio of 3 : 1.

2.1) Changes in pH and alkalinity In the case of control plot under an insufficient alkalinity without organic materials, pH of influent at 7.3-7. 5 was lowered to pH 5. 9- 6. 0 in effluent, while 40% of influent nitrate was removed. The ratio of ASC-produced/ANOs-N reduced, calculated, was 5.5.

As a result of the simultaneous heterotrophic and chemolithoautotrophic denitrification when 1/4T of methanol (Cl) and ethanol (C2) were added, pH levels of effluent were increased up to 6.6 and 6.7, respectively. This increase was presumably due to supply of alkalinity by heterotrophic denitrification.

In the case of control plot without any organic materials in influent, its initial alkalinity (920 mg/L as CaCO3 was depleted by more than 90% and pH was less than 6.0. Thus there was little denitrification reaction due to the significantly reduced activity of sulfur microorganism.

When methanol and ethanol were supplied to each influent, the alkalinity in effluent was more increased than control plot. Under the conditions that 1/4 of theoretical amount was supplied to influent, the alkalinity of methanol and ethanol were maintained by 50% and 60%, respectively. This was presumably due to that ethanol was more adaptable to heterotrophic denitrification than methanol.

2.2) Removal efficiency of nitrate nitrogen and production of sulfate ion Figs. 2 and 3 show the denitrification efficiency of both heterotrophic and chemolithoautotrophic denitrification depending upon the amount of methanol and

ethanol addition.

In the case of sulfur-based denitrification without organic materials, the influent concentration of NO3--N was removed by 40% under the insufficient alkalinity.

When 1/4 T of methanol (Cl) and ethanol (C2) was supplied, the removal efficiency of NOs'-N was increased by 64. 2% and 50. 8%, respectively ; in the case of supplying 1/2T of methanol and ethanol in Columns 1 and 2, the removal efficiency of N03--N in both methanol and ethanol was increased by 93.1 and 73.5%, respectively. Each fraction of heterotrophic denitrification and sulfur-based denitrification was calculated on a basis of AS042-/AN03-N (5.5) obtained in Experiment 1. The fraction of chemolithoautotrophic denitrification in methanol was increased depending upon the increasing amount of methanol, but in the case of ethanol, the fraction was decreased. This was due to the fact that in the case of methanol, as the methanol concentration increased, the formation of C02 and OH-from heterotrophic denitrification reaction increased resulting in enhanced autotrophic denitrification in the range of OT-1/2T of methanol.

In the case of ethanol, the reduced fraction of chemolithoautotrophic denitrification reveals that ethanol contributed much to the high growth of heterotrophic microorganism.

Fig. 4 shows the sulfate production in Columns 1 and 2.

From the formation profile of sulfate ion, its formation was increased in parallel with the supply of methanol, while the formation of sulfate ion was decreased in parallel with the supply of ethanol.

Further, 2,800 mg/L of sulfate ion should be produced when 93% of nitrate nitrogen is removed. Despite the fact that the treatment efficiency for nitrate nitrogen was improved with the addition of 1/2 of the theoretical requirement in Column 1, about 1,900 mg/L of sulfate ion was produced. Thus the formation of sulfate ion can be reduced by the simultaneous autotrophic and heterotrophic denitrification.

2.3) Changes in DOC and turbidity In all cases of Columns 1, and 2, it was revealed that more than 95% DOC was removed in. both materials. This was due to the fact that such organic materials were used for heterotrophic denitrification and for the growth of microorganism. It was noted that ethanol was more advantageous to methanol in terms of the whole

microorganism growth, but the former was inferior to the latter in terms of denitrification. In this respect more amount of ethanol will be required for the maintenance of the same treatment efficiency as methanol.

Effluent cell mass was determined indirectly as turbidity. Turbidity (more than 2.5 NUT) of Column 1 effluent was relatively higher than that of Column 2 (6.5 NTU).

2. 4) Removal of phosphorous To perform the experiment for removal of phosphorous, the actual wastewater containing 250 mg/L of nitrate nitrogen and 20.1 mg/L of phosphorous was used.

The mixture of sulfur particles and shell in the ratio of 3: 1 was added to the sulfur-containing tank and the experiment was performed in the similar manner as above. As a result, it was revealed that nitrate nitrogen was removed by more than 98% at 8 hours (HRT), while phosphorous was removed by about 10 mg/L, showing the removal rate of 40-50%.

Example 2: Changes in pH of burnt and dried shells with the lapse of time Fig. 5 is a graph showing the changes in pH of a mixture containing Ig of shell (1-hour burnt shell at 550oC and shell dried at 105OC) and 50 ml of 0.1 N sulfuric acid with the lapse of time.

The neutralization rate of burnt shell was larger than that of dried shell.

When the tank was wholly neutralized, the shell could maintain the appropriate pH (about 8) for adequate growth of microorganism. In the case of CaO and Ca (OH) 2, extremely rapid reaction occurred and after reaction, inadequate growth pH (12) conditions for microorganism were provided.

Therefore, it is noted that shell may be effectively used in terms of supply of

CO2, a carbon source of chemolithoautotrophic denitrification microorganism, 0 maintenance of pH and removal of phosphorous. Further, the organic materials attached to the dried shell should be removed to the desired level.

As described above, this invention has the following advantages: (1) in addition to the biological denitrification method using sulfur, external carbon source

(methanol, ethanol, acetate, etc.) in small amount (1/3-1/2 of heterotrophic requirement for denitrification) is added so as to perform a simultaneous denitrification process for facultative chemolithoautotrophic, heterotrophic and obligate chemolithoautotrophic denitrification for better denitrification efficiency, (2) insufficient alkalinity during sulfur denitrification can be supplemented using shell or steel slag, while a simultaneous removal process of phosphorous can be made in the presence of calcium ion (Ca2+) in water generated from shell or steel slag by precipitation and (3) the enormously abandoned resources of shell can be recycled, together with steel slag.

Claims

CLAIMS: 1. A simultaneous removal process of nitrogen and phosphorous in wastewater, wherein the wastewater treatment is performed in such a manner that sulfur particles and external carbon source in small amount (1/3-1/2 of heterotrophic requirement for denitrification) are added to a sulfur-containing denitrification tank so as to perform a simultaneous denitrification process for obligate chemolithoautotrophic, facultative chemolithoautotrophic and heterotrophic denitrification, while supplementing the depletion of alkalinity and removing phosphorous through simultaneous addition of shell or steel-making sludge or slag.
2. The simultaneous removal process of nitrogen and phosphorous in wastewater according to claim 1, wherein said external carbon source is selected from methanol, ethanol and acetate.
3. The simultaneous removal process of nitrous nitrogen and phosphoroous in wastewater according to claim 1 or claim 2, wherein said shell or steel-making sludge/slag is added to the reactor in such a manner that sulfur and shell or steel-making sludge/slag are mixed in the ratio of 4 : 1-2 : 1.
4. The simultaneous removal process of nitrogen and phosphorous in wastewater according to any preceding claim, wherein said shell is selected from a burnt or dried shell.
5. The simultaneous removal process of nitrogen and phosphorous in wastewater according to claim 4, wherein said shell is a burnt shell.