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Removal of nitrogen and phosphorus from swine wastewater by the activated sludge units with the intermittent aeration process
Wat. Res. Vol. 25, No. 11, pp. 137%1388, 1991 Printed in Great Britain.All rights reserved
0043-1354/91 $3.00+0.00 Copyright © 1991PergamonPressplc
REMOVAL OF NITROGEN A N D PHOSPHORUS FROM SWINE WASTEWATER BY THE ACTIVATED SLUDGE UNITS WITH THE INTERMITTENT AERATION PROCESS TAKASHIOSADA1, KIYONORIHAGA2 and YASUOHARADA2 tLaboratory of Animal Waste Management, National Institute of Animal Industry, Ministry of Agriculture, Forestry and Fisheries, 2 Ikenodai, Kukizaki, Inashiki-gun, Ibaraki 305 and 2National Institute of Agre-Envirnnmental Sciences, Ministry of Agriculture, Forestry and Fisheries, 3-1-3 Kannondai, Tsukuba, Ibaraki 305, Japan (First received June 1990; accepted in revised form April 1991) Abstract--Nitrogen and phosphorus removal in fill-and-draw type activated sludge units with an intermittent aeration process (IAP) was evaluated with typical wastewater from swine housing (total N/BOD5 ratios were 0.18, 0.31 and 0.45), in comparison with a non-limited aeration process (a conventional process, NLAP), under 0.50kg m -3 d -t BOD loading for each unit in bench scale. Operational conditions for the units were the same except for the aeration program; in the NLAP, a conventional consecutive aeration for 21 h was adopted, whereas in the lAP, aeration was intermittent and aeration and non-aeration periods were alternated at intervals of 1.0 h (IAP-1.0) or 3.5 h (IAP-3.5). When the units were high in MLSS concentrations, high removal efficiencies(89.0-99.5%) for BOD and TOC were attained with both IAP and NLAP in all runs. While, large differences in the removal of nitrogen and phosphorus between IAP and NLAP were observed; at influent N/BOD5 of 0.18, removal efficienciesfor total nitrogen in IAP-I.0 and NLAP were 96.9 and 58.6%, and for total phosphorus were 80.8 and 47.8%, respectively. However, those removal efficiencies decreased with the increase in the N/BOD5 ratio of wastewater charged. Removal efl~cienciesfor total nitrogen in IAP-1.0 was 72.2%, even at influent N/BOD 5 of 0.45. Thus, high removal efficiencies for organic substances, nitrogen and phosphorus in swine wastewater were simultaneously obtained by IAPs. By adopting an adequate aeration program for individual swine wastewater treatment, this system will provide a promising means for nitrogen and phosphorus control without pH control, divided change of wastewater or addition of methanol. Key words--animal waste, wastewater treatment, a fill-and-draw type unit, intermittent aeration, nitrification, denitrification, N/BOD ratio, biological P removal
INTRODUCTION
Animal wastes containing nutrients such as nitrogen, phosphorus and potassium at high concentrations have been widely used for fertilizer. With the present trend toward raising a large herd of livestock in a more restricted area, it is difficult to apply all of the wastes to cropland. Wastewater handling is especially troublesome and has to be treated carefully to prevent water pollution when discharged. In the last two decades, much effort has been made to study not only the anaerobic digestion of animal wastewater (Chen et al., 1988; Chayovan et al., 1988; Sneath, 1988; Ng and Chin, 1988; Safley and Westerman, 1989) but the aerobic degradation treatment (Honda, 1974; Honda et al., 1974; Kameoka et al., 1985), obtaining high removal efficiencies for BOD, TOC and SS. However, only a few studies have dealt with nitrogen and phosphorus removal from animal wastewater, which are currently of great interest in terms of eutrophication of streams and lakes. De la Noue and Basseres (1989) achieved a high rate removal of NH4-N and PO4P from anaerobically digested swine manure with
microalgae: the effluent of the digester was diluted with tap water to obtain initial manure concentrations of 0.6-3.0% (NH4-N, 19.8-98.8mg 1-1). Svoboda and FaUowfield (1989) conducted a highrate algal pond treatment, after several pretreatments, for piggery slurry. As this treatment requires a long hydraulic retention time, an adequate dilution and a shallow algal pond of large area was needed for the treatment. We reported previously that the activated sludge process with limited aeration (LAP) is effective for swine wastewater (Osada et al., 1989): high removal efficiencies for BOD, TOC and total nitrogen were achieved with LAP. However, it could not satisfy the effluent standard for nitrogen because swine wastewater contains a large amount of nitrogen which corresponds to 20-40% of BOD (Haga et al., 1989). The time course profile during LAP operation indicated that nitrification activity decreased gradually, as the pH of treated wastewater dropped due to the resultant oxidized nitrogen (NO~-N). Little work has been done to develop the treatment of such wastewater without pH control. To attain a higher removal efficiency for nitrogen, we adopted another aeration
1377
TAKASHI OSADA et al.
1378
Table 1. Characteristics of the prepared swine wastewater* fed into the individual runs
p r o g r a m , the i n t e r m i t t e n t a e r a t i o n p r o c e s s ( l A P ) , to a v o i d a c c u m u l a t i n g N O x - N a n d affecting B O D r e m o v a l a n d nitrification activity. T h i s s t u d y deals w i t h the l A P for swine w a s t e w a t e r w h i c h is especially rich in n i t r o g e n a n d p h o s p h o r u s , in a n a t t e m p t to e v a l u a t e the a d v a n t a g e o f the l A P to typical w a s t e w a t e r in swine h u s b a n d r y .
Items pH TS SS BOD TOC Total N TKN NH4-N NOx-N Total P PO4-P CI
MATERIALS AND METHODS
Equipments and wastewater Six bench-scale activated sludge units were set up in parallel in a chamber kept at 20 _+ I°C. The experimental apparatus used was the same as our previous report (Osada et al., 1989). A 3 I. graduated cylinder was used as the aeration tank. The operating volume was 2 1. Air was fed through a stone diffuser at the bottom of the aeration tank. The wastewater was prepared from swine feces and urine. Swines were fed in stainless cages in order to collect feces and urine separately. Urine and feces at three different periods were weighed and mixed respectively, and the mixtures were sieved (32 mesh, 0.5 mm), to obtain three kinds of swine wastewater. Table 1 shows the chemical characteristics of the wastewater. The total nitrogen/BOD s (N/BOD) ratio of the wastewater fed in Runs 1 and 2 was approx. 0.18 and similar to that from most swine houses with flat type floors. That of the wastewater fed in Run 4 was approx. 0.45 and similar to that from swine houses with slatted floors. The wastewater was stored at 4°C and diluted with tap water according to each experimental condition prior to the treatment. Constitutents o f the influent for each run are shown in Table 2 including the treatment result. The wastewater was stored at 4°C for 2 months after which more than 95% of the initial amounts of BODs, TN and TP was retained. Operation Three types of operation were conducted in duplicate. In the NLAP, a conventional consecutive aeration for 21 h was adopted, while in the IAP, aeration was intermittent and aeration and non-aeration periods were alternated at intervals of 1.0h (IAP-I.0) and 3.5h (IAP-3.5) (Fig. I). The aeration programs for the units started just after daily charging. The aeration rate during the aeration periods was 0.651 min -~ and forced agitation was not applied. After the
Units
Runs I and 2
Run 3
Run 4
mg I i mg I ~ mgO21-I mg I i mgl ~ mg 1 ~ mg I ~ mg I ~ mgl ~ mg I ~ mg 1- ~
8.5 21,760 10,050 I0,000 3680 1840 I840 790 ND 1070 895 560
9.0 16,882 8421 9000 4175 2814 2814 1919 tr 770 86 443
9.1 16,432 6388 10,000 4426 4498 4498 3535 tr 529 461 806
N/BOD P/BOD
0.18 0. l 1
0.31 0.09
*Prepared swine wastewater (original) had been stored until use at 4°C. Prior to the feeding it was diluted with water to give the prescribed BOD loading rate. aeration programs had been performed, the contents in the units were allowed to settle for 2h, to be discharged manually. After 667 ml of supematant over the mixed liquor suspended solids (MLSS) in each unit was withdrawn, the same volume of wastewater was manually charged in a minute (Fig. 1). BOD loading of Runs 1, 3 and 4 and Run 2 was 0.50kg BOD m -3 d -I and 0.75 kg BOD m -3 d -~, respectively. The hydraulic retention time (HRT) was 3 days. The activated sludge seed was obtained from the aeration tank of the activated sludge system in our institute. Excess sludge was removed once a week for the adjustment of the MLSS concentration. Each unit was operated for a period longer than two sludge ages (35-38 days) before steady-state conditions were obtained. The performance of each unit was evaluated for 44i weeks at the steady state.
Analysis The effluent from the units was analyzed for pH and transparency daily, and for BODs, TOC, TN, NH4-N, NO2-N, N O 3-N, TP and PO 4-P two or three times a week. TOC was determined by a TOC analzyer (Beckman 102 model). NO2-N, NO3-N and PO4-P were determined by ion chromatography ( D I O N E X system 14) and NH4-N was analyzed by Bremners' method (Bremner and Keeney, 1965). TN and TP was measured by flow injection analysis (Haga et al., 1988) based on the persulfate digestion method
Table 2. The mean (.~) and SD of the treatment data in the experiment
Effluent NLAP
IAP-1.0
IAP-3.5
Influent (rag I-i)
(rag I- t) .~ SD
Removal*
(rag I i) g SD
Removal*
I
TOC Total N Total P
552 276 160
25.7 + 1.5 114.4 + 13.6 83.5 + 16.1
95.3% 58.6% 47.6%
26.5 + 0.4 8,5 + 8.5 30,7 _+ 1.6
95.2% 96.9% 80.8%
33.9 + 3.3 24.4 _+22.6 31.1 -+ 1.4
93.9% 91.2% 80.6%
2
TOC Total N Total P
828 414 240
36.5 + 5.7 157.7 + 8.8 116.4_+7.6
95.6% 61.9% 51.1%
35.4 _+6,7 8,4 _+2.7 21,3_+ 6.9
95.7% 98.0% 91.1%
39.6 + 6.6 14.6 _+8.0 27.6_+8.7
95.3% 96,5% 88.5%
3
TOC Total N Total P
690 465 127
75.9 _+8.5 236.0 _+ 10.0 131.5 -+ 18.4
89.0% 49.2% --
54,0 _+ 1.8 21,0 _+7.1 63,8 -+ 6.1
92.1% 95.5% 49.8%
No experiment
4
TOC Total N Total P
664 674 79
64.4 _+4.5 504.0 _+ 1.2 82.9_+2.5
90.3% 25.2% --
56,2 _+3.5 187.5 _+ 19.9 64.3_+8.5
91.5% 72.2% 18.6%
53.8 _+0.5 91.9% 192.4 _+6.4 71.5% 63.3_+10.0 19.9%
Run Items
*Removal efflciencies in the tables were calculated as: total E removal (%) = ~ x 100. Total h total amount of pollutant in daily influent. Total E: total amount of pollutant in daily effluent.
0.45 0.05
(rag I ') £ SD
Removal*
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Nutrient removal in activated sludge units
Time 0 2 4 6 8 I0 12 14 16 18 202224(0)
N Sedimentn L Discharge A Chorge P Aeration t Sedimentnj A Discharge
~I
IPo Charge
Aerotior, ~ ~ ~ m ~] ~ ~ ~ ~I
Sedimentn At Dischar9e P Charge :5.5 Aeration
I ~
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Fig. 1. Time chart of experimental operation. NLAP, non-limited aeration process; IAP, intermittent aeration process.
(Langner and Hcndrix, 1982). A scmi-micro-Kjeldahl method was applied of the original wastewater to detect deterioration during stock periods. SS, MLSS and MLVSS was measured weekly. All analyses made were in accordance with the procedures of APHA (1985). In the time course of each treatment, pH, DO, TOC, TN, NH4-N, NO2-N, NO3-N, TP and PO4-P was measured to follow the reduction process for nitrogen and phosphorus. Samples were centrifuged at 3000 rpm for 5 rain and the supernatant samples were subjected to the analyses. MLSS, MLVSS and TN and TP of activated sludge were determined just before and after the time course measurements.
RESULTS AND DISCUSSION Two types of data were obtained. The first was the set of routine data from samples collected from each unit two or three times a week at steady-state operation. These data defined the average performance of each unit based on the concentrations of the pollutants in the influent and effluent. The other data were collected along the time course of treatments on the last day of the collection period of the above sample. The time course profile was obtained to find the effect
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Fig. 2. Comparison of the NLAP and IAP-I.0 operations in Run 1 (BOD loading = 0.50 kg m -3 d-~; N/BOD = 0.18). (a) Changes of pH, DO and TOC with the NLAP. (b) Changes of nitrogen with the NLAP. (c) Changes of pH, DO and TOC with the IAP-I.0. (d) Changes of nitrogen with the IAP-I.0.
Nutrient removal in activated sludge units of the appropriate aeration and non-aeration periods on the treatment. Percent settled sludge volumes after 2 h sedimentation were kept below 40% at a MLSS concentration of 8500-9000 mg l -~ (Runs l, 3 and 4) and 60% at a MLSS concentration of 13,000-14,000mg 1-1 (Run 2) for all units. Each unit of Runs l, 2, 3 and 4 was operated at sludge ages of 17.5, 17.9, 17.7 and 18.9 days, respectively. The sludge retention time (SRT) of all the units was consequently almost 30 days. In this experiment, little difference was observed between IAP-1.0 and IAP-3.5 for the treatment results. So, we hereafter regarded IAP-I.0 as a representative IAP.
1381
BOD, TOC and SS removals High removal efficiencies (89.0-99.5%) for BOD, TOC and SS were attained with both IAP and NLAP in all runs. TOC of the effluent is shown in Table 2. High MLSS concentrations in the units may explain the above performances. In fact, the food-tomicrooganism ratio (F/M) in those units was low (0.054-0.059 g BODs (g MLSS)-~). TOC concentration profiles for each unit are presented in Figs 2, 3, 4 and 5. TOC reduction occurred immediately after the aeration in all runs and the reduction was observed even at the first non-aeration period in the IAP. At the earlier stage of the non-aeration period in the IAP operation, a little increase of
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1382
TAKASHIOSADAet al.
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Fig. 3. Comparison of the NLAP and IAP-1.0 operations in Run 3 (BOD loading =0.50kg m -~ d t; N/BOD = 0.31). (a) Changes of pH, DO and TOC with the NLAP. (b) Changes of nitrogen with the NLAP. (c) Changes of pH, DO and TOC with the IAP-I.0. (d) Changes of nitrogen with the IAP-I.0. TOC concentration appeared especially in Run 2 [Fig. 5(a)]. No difference was found between Run 1 (BOD 0.50 kg m -3 d -1) and Run 2 (BOD 0.75 kg m -3 d -a) for BOD, TOC and SS removal etticiencies. Those removal efficiencies at BOD 0.50 kg m -3 d loading were slightly affected by increasing the N/BOD ratio of the influent. Nitrogen removal
Large differences in the removal of nitrogen were observed between IAP and NLAP (Table 2). Removal efficiencies of the lAP (71.5-98.0"/o) were much higher than that of the NLAP (25.2-61.9%). Figure 2(a) and (b) shows the profiles of pH, DO and TOC and nitrogen in Run 1 of NLAP. Though
organic nitrogen and NH4-N in influent were readily oxidized, a noticeable decrease of total nitrogen during the NLAP operation did not occur. When the N/BOD ratio of influent was increased to 0.31, NH4-N was not readily oxidized, due to the accumulation of NOx-N and the concomitant drop in pH [Fig. 3(a) and (b)]. Some organisms are reported to undergo a single stage nitrification-denitrification (aerobic-anoxic) in which organic material in the influent is utilized as the electron donor for the denitrification reaction (Applegate et al., 1980; Kakiichi et al., 1988), however, these authors did not envisage the above problem, because the N/BOD ratio of the influent used was relatively low (0.10-0.12). The incorporation of
Nutrient removal in activated sludge units
1383
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Fig. 4. Changes of (a) pH, DO and TOC, and Co)nitrogen during the IAP-1.0 operation in Run 4 (BOD loading = 0.50 kg m -3 d-I; N/BOD = 0.45). the intermittent non-aeration period in the IAP avoided the accumulation of NOx-N to attain high nitrogen removal in all runs. Extremely high removal (95% above) was achieved with the IAP-I.0 (especially in Runs 1, 2 and 3). Figures 2(d) and 3(d) show the nitrogen profle with the IAP-1.0 in Runs 1 and 3, respectively. NOx-N produced during an aeration period was immediately reduced in the subsequent non-aeration period to nitrogen gas, and nitrification in the aeration periods occurred smoothly [Figs 2(d) and 3(d)] under the stable pH conditions [Figs 2(c) and 3(c)]. Thus, along with the proceeding NH4-N oxidation, total nitrogen and NO~-N decreased in the lAP operation. Warner et al. (1986) reported on the application of the general kinetic model for denitrification in anoxic-aerobic digestion of excess sludge wasted
from the activated sludge process. They described that the stability of alkalinity and pH is a major advantage over purely aerobic digestion. Our results on the animal wastewater show the same advantage over nitrification and denitrification [Figs 2(c) and 3(c)]. Denitrification occurs in anoxic conditions with the existence of organic matter as electron donor. Methanol added to and/or organic matter contained in the influenthave been used for this objective.Thus, in the case of the IAP, denitrification might occur mainly at the earlierstage of the non-aeration period in the operation when organic material in the influent stillremains in the mixed liquor. However, our results showed that denitrificationoccurred mainly after the T O C profilehad already reached steady-state at a low level of T O C concantration [Figs 2(c), 2(d), 3(c), 3(d)
1384
TAKASH10SADAet al.
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- I0-12 14 16 18 20-22 T i m e in h o u r s Fig. 5. Changes of (a) pH, DO and TOC, and (b) nitrogen during the IAP-1.0 operation in Run 2 (BOD loading = 035 kg m -3 d-t; N/BOD = 0.18).
and 5]. It suggests that TOC is removed from mixed liquor by adsorption on the surface of the activated sludge or its reservoir in microbial cells and the TOC is then used again for denitrification. Further study is needed to clarify the mechanisms of such denitrification at low TOC. Wiiderer et al. (1987) observed the difference in microbial nitrite reduction rates in the presence of glucose or acetate during anoxic conditions. Investigation of organic matters in wastewater is necessary to assess the limitation for nitrogen removal without any supplemental carbon source. At Run 2, under 0.75 kg m -3 d - t of BOD loading, nitrogen was mainly decreased during the aeration period in the early stage of the lAP operation when the DO stayed at a low level [Fig. 5(b)]. Applegate et al. (1980) assumed that most of the denitrification occurred in the first two channels under low oxygen concentrations (DO 0.1-0.9 ml 1-l) in a multi-channel
oxidation ditch system. What types of nitrogenous gases were released during the denitrification process remains unsolved. Phosphorus removal
Removal efliciencies for phosphorus with the lAP were higher than those with the NLAP (Table 2). A high rate of removal of 91% was achieved in Run 2 and we confirmed that the removal phenomenon was composed of the release of phosphorus during the non-aeration periods and of the excess uptake of phosphorus in the aeration periods [Fig. 6(b)], however, this was not clear with N L A P [Fig. 6(a)]. A similar phenomenon has been reported by Levin et al, (1965) and Shapiro et aL (1967). Accumulation of phosphorus in activated sludge was observed in the lAP. Excess sludge on the last day in Run 2 contained 6.5% of phosphorus on a dry matter basis, which was
Nutrient removal in activated sludge units higher than that of the NLAP (4.3%). Gradual increase of phosphorus in the water treated by the NLAP [Fig. 6(a) and (c)] seemed to result from the release of phosphorus from activated sludge. At Run 4, the phosphorus profile during IAP-1.0 operation showed the same tendency as that of the NLAP operation [Fig. 6(c) and (d)].
1385
mated to be 0.2-0.4 (Haga et aL, 1989), the application of the IAP for swine wastewater treatment might anticipate the removal of nitrogen to satisfy the effluent standards. When the N/BOD ratio of the influent increased to 0.31 (Run 3) and 0.45 (Run 4), phosphorus removal efflciencies with the IAP-1.0 decreased to 49.8 and 18.9%, respectively (Fig. 7), though the P/BOD ratio of the influent was lower (Table 1). Barnard (1976) reported that the presence of NO~-N disturbed the release of phosphorus during the non-aeration period, as did the presence of molecular oxygen, and diminished the uptake of phosphorus during the aeration period. In our experiments, those disturb ances were observed with the NOx-N concentration not only in Run 4, but in Run 3. In order to achieve
N/BOD ratio and the removal of nitrogen and phosphorus The relationship between the N/BOD ratio of the wastewater and the removal of nitrogen and phosphorus is summarized in Fig. 7. Nitrogen removal efficiencies were nearly constant up to an N/BOD ratio of 0.31, and decreased with an increase in the ratio. As the N/BOD of swine wastewater was esti-
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TAKASmOSADAet al.
1386
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Time in hours Fig. 6 (c) and (d) Fig. 6. Changes of total P and PO4-P during the NLAP and lAP-1.0 operations. (a) NLAP and (b) lAP-1.0 in Run 2 (BOD loading = 0.75 kg m -3 d-l; N/BOD = 0.18). (c) NLAP and (d) IAP-I.0 in Run 4 (BOD loading = 0i50 kg m -3 d-t; N/BOD = 0.45).
a higher removal for phosphorus it is essential to attain almost complete removal of nitrogen by a single-sludge system such as the lAP. At the end of the aeration period, nitrogen was mainly detected as NO 2-N with the lAP operation in Run 3 at a higher N/BOD ratio (0.31), though both NO 2-N and NO~-N were found in Run 1 at a lower N/BOD ratio (0.18) [Figs 2(d) and 3(d)]. Turk et al. (1989) reported on the advantage of the shortened pathway that bypassed the nitrite oxidation step to nitrate and the subsequent nitrate reduction step to nitrite by free-ammonia (NH3). The most remarkable advantage may be the high nitrogen removal via the intermediary nitrites (NO2-N). However, when the N/BOD ratio of the influent in the IAP-1.0 was as high as 0.45, the nitrogen removal efficiency decreased to approx. 72% (Table 2). NOx-N, which built up during the aeration period, was partly
reduced to nitrogen gas at the next non-aeration period [Fig. 4(a)]. As a result, NO2-N accumulation occurred and the pH of the unit declined to 6.3 [Fig. 4(b)]. Feasibility o f the l A P .[or swine farms
The fill-and-draw type activated sludge system is widely used in swine farms which have only a limited area in the suburbs. The operational conditions for these experiments were mostly the same as the actual one; for example, once-a-day charge and discharge, 3 days of HRT and the characteristics of the influent (Haga et al., 1989). Taking into account the economical aeration and ease of application (just changing the aeration program with a timer) on the lAP, this system will provide a promising means for nitrogen and phosphorus control in animal wastewater.
Nutrient removal in activated sludge units
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.
.
.
.
.
.
.
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Acknowledgements--The authors would like to thank Dr H. Tanaka for helpful comment on and critical reading of the manuscript, and Drs H. Mayumi, M. Kawaguchi and M. Yonaga for stimulating discussion, all of National Institute of Animal Industry, Japan. This work was supported in part by the Project "Research and Development on the Techniques for the Removal of Nitrogen and Phosphorus from Livestock Wastewater" (FY1984-1988), Environment Agency, Government of Japan, for which the authors express their thanks.
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REFERENCES
/
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o.5
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1387
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N / B O D Ratio Fig. 7. Effect of the N/BOD ratio of the influent wastewater on the removal efficiencyof nitrogen and phosphorus with the NLAP and IAP-1.0 treatments under 0.50 kg m -3 d -~ BOD loading. - - O - - , N removal with the IAP-1.0; - - I - - , N removal with the NLAP; ---C)---, P removal with the IAP-I.0, ---[]---, P removal with the NLAP. CONCLUSIONS The experiments in a fill-and-draw type activated sludge unit in a single tank system have been performed with both the IAP and NLAP operations on some typical wastewater prepared from swine feces and urine. The following results were obtained. (1) BOD, TOC and SS removal efficiencies with the lAP operation were as high as those with the NLAP for all wastewater used, though the total aeration period in the lAP were nearly half of that of the NLAP. (2) In the removal of nitrogen and phosphorus, large differences between the lAP and NLAP were observed under a BOD loading of 0.50kg m -3 d -l without any supplemented carbon sources and pH stabilizers. (a) At an influent N/BOD ratio of 0.18, removal efficiencies for total nitrogen in the IAP-1.0 and NLAP were 96.9 and 58.6%, and for total phosphorus were 80.8 and 47.8%, respectively. Along with NH4-N oxidation (aeration periods), total nitrogen and NOx-N decreased in the lAP operation. As a result, extremely high nitrogen removal by the lAP was accomplished. Under these conditions, phosphorus removal occurred with the release of phosphorus during the non-aeration periods followed by the excess uptake of phosphorus during the aeration periods in the activated sludge. (b) At a higher influent N/BOD ratio of 0.31, the removal efficiency for total nitrogen in the IAP-I.0 was 95.5%, but that for phosphorus was 49.8%. (c) At an even higher influent N/BOD ratio of 0,45, removal efficiencies for nitrogen and phosphorus in the IAP-I.0 were 72.2 and 18.6%, respectively.
APHA (1985) Standard Methods for the Examination o f Water and Wastewater, 16th edition. American Public Health Association, Washington, D.C. Applegate C. S., Wilder B. and DeShaw J. R. (1980) Total nitrogen removal in a multi-channel oxidation system. J. Wat. Pollut. Control Fed. 52, 568-577. Barnard J. L. (1976) A review of biological phosphorus removal in the activated sludge process. Water Sth Afr. 2, 136-144. Bremner J. M. and Keeney D. R. (1965) Steam distillation methods for determination of ammonium, nitrate and nitrite. Analyt. chim. Aeta 32, 485-495. Chayovan S., Gerrish J. B. and Eastman J. A. (1988) Biogas production from dairy manure: the effect of temperature pertubation. Biol. Wastes 25, 1-16. Chen T. H., Day D. L. and Steinberg M. P. (1988) Methane production from fresh versus dry dairy manure. Biol. Waste 24, 297-306. Haga K. Osada T. and Harada Y. (1988) Flow injection analysis for the determination of total nitrogen and total phosphorus in animal wastewater. J. Jpn. Swge Wks Assoc. 25(286), 74-80 (in Japanese). Haga K., Osada T. and Harada Y. (1989) Characterization of piggery wastewater and the control of nitrogen and phosphorus. Envir. Inform. Sei. 18, 57q50 (in Japanese). Honda K. (1974) Treatment of the wastewater from animal housing by the oxidation ditch system. Technical Report No. 3 (Research Council Secretariat), Ministry of Agriculture, Forestry and Fisheries (in Japanese). Honda A., Ito H. and Kawakita T. (1974) Swine waste treatment by worm through medium board. J. Wat. Waste 16, 1129-1140 (in Japanese). Kakiichi N., Kamata S, lto O., Yamano S. and Uchida K. (1988) Relationship between gentle stirring time and simultaneous removal of nitrogen and phosphorus from swine wastewater by modified aerated lagoon process. Jpn. J. Zooteehnol. Sei. 59, 1027-1033. Kameoka T., Kagi T., Sakimoto M. and Inno Y. (1986) Characteristics of concentrated wastewater treatment of swine by the rotating disc system. Jpn. J. Zooteehnol. Sei. 57, 209-215 (in Japanese). Langner C. L. and Hendrix P. F. (1982) Evaluation of a persulfate digestion method for particulate nitrogen and phosphorus. Wat. Res. 16, 1451-1454. Levin G. V. and Shapiro J. (1965) Metabolic uptake of phosphorus by wastewater organisms. J. Wat. Pollut. Control Fed. 37, 800-821. Ng W. J. and Chin K. K. (1988) Treatment of piggery wastewater by expanded-bed anaerobic filters. Biol. Waste 26, 215-228. de la Noue J. and Basseres A. (1989) Biotreatment of anaerobically digested swine manure with microalgae. Biol. Waste 29, 17-31. Osada T., Haga K. and Harada Y. (1989) Removal of nitrogen from swine wastewater by limited aeration process. Jpn. J. Wat. Pollut. Res. 12, 122-130 (in Japanese). Safley L. M. Jr and Westerman P. W. (1989) Anaerobic lagoon biogas recovery systems. Biol. Waste 27, 43~52.
1388
TAKASHI OSADAel al.
Shapiro J., Levin G. V. and Humberto Z. G. (1967) Anoxically induced release of phosphorus in wastewater treatment. J. War. Pollut. Control Fed. 39, 1810-1818. Sheath R. W. (1988) The effect of removing solids from aerobically treated piggery slurry on the VFA levels during storge. Biol. Waste 26, 175--188. Svoboda I. F. and Fallowfield H. J. (1989) An aerobic piggery slurry treatment system with integrated heat recovery and high-rate algal ponds. War. Sci. Technol. 21, 277-287.
Turk O. and Mavinic D. S. (1989) Stability of nitrogen build-up in an activated sludge system. J. Wat. Pollut. Control Fed. 61, 1440-1448. Warner A. P. C., Ekama G. A. and Marais G. V. R. (1986) The activated sludge process--4, application of the general kinetic model to anoxic-aerobic digestion of waste activated sludge. Wat. Res. 20, 943-958. Wilderer P. A., Jones W. L. and Dau U. (1987) Competition in denitrification systems affecting reduction rate and accumulation of nitrogen. Wat. Res. 21, 239-245.
0043-1354/91 $3.00+0.00 Copyright © 1991PergamonPressplc
REMOVAL OF NITROGEN A N D PHOSPHORUS FROM SWINE WASTEWATER BY THE ACTIVATED SLUDGE UNITS WITH THE INTERMITTENT AERATION PROCESS TAKASHIOSADA1, KIYONORIHAGA2 and YASUOHARADA2 tLaboratory of Animal Waste Management, National Institute of Animal Industry, Ministry of Agriculture, Forestry and Fisheries, 2 Ikenodai, Kukizaki, Inashiki-gun, Ibaraki 305 and 2National Institute of Agre-Envirnnmental Sciences, Ministry of Agriculture, Forestry and Fisheries, 3-1-3 Kannondai, Tsukuba, Ibaraki 305, Japan (First received June 1990; accepted in revised form April 1991) Abstract--Nitrogen and phosphorus removal in fill-and-draw type activated sludge units with an intermittent aeration process (IAP) was evaluated with typical wastewater from swine housing (total N/BOD5 ratios were 0.18, 0.31 and 0.45), in comparison with a non-limited aeration process (a conventional process, NLAP), under 0.50kg m -3 d -t BOD loading for each unit in bench scale. Operational conditions for the units were the same except for the aeration program; in the NLAP, a conventional consecutive aeration for 21 h was adopted, whereas in the lAP, aeration was intermittent and aeration and non-aeration periods were alternated at intervals of 1.0 h (IAP-1.0) or 3.5 h (IAP-3.5). When the units were high in MLSS concentrations, high removal efficiencies(89.0-99.5%) for BOD and TOC were attained with both IAP and NLAP in all runs. While, large differences in the removal of nitrogen and phosphorus between IAP and NLAP were observed; at influent N/BOD5 of 0.18, removal efficienciesfor total nitrogen in IAP-I.0 and NLAP were 96.9 and 58.6%, and for total phosphorus were 80.8 and 47.8%, respectively. However, those removal efficiencies decreased with the increase in the N/BOD5 ratio of wastewater charged. Removal efl~cienciesfor total nitrogen in IAP-1.0 was 72.2%, even at influent N/BOD 5 of 0.45. Thus, high removal efficiencies for organic substances, nitrogen and phosphorus in swine wastewater were simultaneously obtained by IAPs. By adopting an adequate aeration program for individual swine wastewater treatment, this system will provide a promising means for nitrogen and phosphorus control without pH control, divided change of wastewater or addition of methanol. Key words--animal waste, wastewater treatment, a fill-and-draw type unit, intermittent aeration, nitrification, denitrification, N/BOD ratio, biological P removal
INTRODUCTION
Animal wastes containing nutrients such as nitrogen, phosphorus and potassium at high concentrations have been widely used for fertilizer. With the present trend toward raising a large herd of livestock in a more restricted area, it is difficult to apply all of the wastes to cropland. Wastewater handling is especially troublesome and has to be treated carefully to prevent water pollution when discharged. In the last two decades, much effort has been made to study not only the anaerobic digestion of animal wastewater (Chen et al., 1988; Chayovan et al., 1988; Sneath, 1988; Ng and Chin, 1988; Safley and Westerman, 1989) but the aerobic degradation treatment (Honda, 1974; Honda et al., 1974; Kameoka et al., 1985), obtaining high removal efficiencies for BOD, TOC and SS. However, only a few studies have dealt with nitrogen and phosphorus removal from animal wastewater, which are currently of great interest in terms of eutrophication of streams and lakes. De la Noue and Basseres (1989) achieved a high rate removal of NH4-N and PO4P from anaerobically digested swine manure with
microalgae: the effluent of the digester was diluted with tap water to obtain initial manure concentrations of 0.6-3.0% (NH4-N, 19.8-98.8mg 1-1). Svoboda and FaUowfield (1989) conducted a highrate algal pond treatment, after several pretreatments, for piggery slurry. As this treatment requires a long hydraulic retention time, an adequate dilution and a shallow algal pond of large area was needed for the treatment. We reported previously that the activated sludge process with limited aeration (LAP) is effective for swine wastewater (Osada et al., 1989): high removal efficiencies for BOD, TOC and total nitrogen were achieved with LAP. However, it could not satisfy the effluent standard for nitrogen because swine wastewater contains a large amount of nitrogen which corresponds to 20-40% of BOD (Haga et al., 1989). The time course profile during LAP operation indicated that nitrification activity decreased gradually, as the pH of treated wastewater dropped due to the resultant oxidized nitrogen (NO~-N). Little work has been done to develop the treatment of such wastewater without pH control. To attain a higher removal efficiency for nitrogen, we adopted another aeration
1377
TAKASHI OSADA et al.
1378
Table 1. Characteristics of the prepared swine wastewater* fed into the individual runs
p r o g r a m , the i n t e r m i t t e n t a e r a t i o n p r o c e s s ( l A P ) , to a v o i d a c c u m u l a t i n g N O x - N a n d affecting B O D r e m o v a l a n d nitrification activity. T h i s s t u d y deals w i t h the l A P for swine w a s t e w a t e r w h i c h is especially rich in n i t r o g e n a n d p h o s p h o r u s , in a n a t t e m p t to e v a l u a t e the a d v a n t a g e o f the l A P to typical w a s t e w a t e r in swine h u s b a n d r y .
Items pH TS SS BOD TOC Total N TKN NH4-N NOx-N Total P PO4-P CI
MATERIALS AND METHODS
Equipments and wastewater Six bench-scale activated sludge units were set up in parallel in a chamber kept at 20 _+ I°C. The experimental apparatus used was the same as our previous report (Osada et al., 1989). A 3 I. graduated cylinder was used as the aeration tank. The operating volume was 2 1. Air was fed through a stone diffuser at the bottom of the aeration tank. The wastewater was prepared from swine feces and urine. Swines were fed in stainless cages in order to collect feces and urine separately. Urine and feces at three different periods were weighed and mixed respectively, and the mixtures were sieved (32 mesh, 0.5 mm), to obtain three kinds of swine wastewater. Table 1 shows the chemical characteristics of the wastewater. The total nitrogen/BOD s (N/BOD) ratio of the wastewater fed in Runs 1 and 2 was approx. 0.18 and similar to that from most swine houses with flat type floors. That of the wastewater fed in Run 4 was approx. 0.45 and similar to that from swine houses with slatted floors. The wastewater was stored at 4°C and diluted with tap water according to each experimental condition prior to the treatment. Constitutents o f the influent for each run are shown in Table 2 including the treatment result. The wastewater was stored at 4°C for 2 months after which more than 95% of the initial amounts of BODs, TN and TP was retained. Operation Three types of operation were conducted in duplicate. In the NLAP, a conventional consecutive aeration for 21 h was adopted, while in the IAP, aeration was intermittent and aeration and non-aeration periods were alternated at intervals of 1.0h (IAP-I.0) and 3.5h (IAP-3.5) (Fig. I). The aeration programs for the units started just after daily charging. The aeration rate during the aeration periods was 0.651 min -~ and forced agitation was not applied. After the
Units
Runs I and 2
Run 3
Run 4
mg I i mg I ~ mgO21-I mg I i mgl ~ mg 1 ~ mg I ~ mg I ~ mgl ~ mg I ~ mg 1- ~
8.5 21,760 10,050 I0,000 3680 1840 I840 790 ND 1070 895 560
9.0 16,882 8421 9000 4175 2814 2814 1919 tr 770 86 443
9.1 16,432 6388 10,000 4426 4498 4498 3535 tr 529 461 806
N/BOD P/BOD
0.18 0. l 1
0.31 0.09
*Prepared swine wastewater (original) had been stored until use at 4°C. Prior to the feeding it was diluted with water to give the prescribed BOD loading rate. aeration programs had been performed, the contents in the units were allowed to settle for 2h, to be discharged manually. After 667 ml of supematant over the mixed liquor suspended solids (MLSS) in each unit was withdrawn, the same volume of wastewater was manually charged in a minute (Fig. 1). BOD loading of Runs 1, 3 and 4 and Run 2 was 0.50kg BOD m -3 d -I and 0.75 kg BOD m -3 d -~, respectively. The hydraulic retention time (HRT) was 3 days. The activated sludge seed was obtained from the aeration tank of the activated sludge system in our institute. Excess sludge was removed once a week for the adjustment of the MLSS concentration. Each unit was operated for a period longer than two sludge ages (35-38 days) before steady-state conditions were obtained. The performance of each unit was evaluated for 44i weeks at the steady state.
Analysis The effluent from the units was analyzed for pH and transparency daily, and for BODs, TOC, TN, NH4-N, NO2-N, N O 3-N, TP and PO 4-P two or three times a week. TOC was determined by a TOC analzyer (Beckman 102 model). NO2-N, NO3-N and PO4-P were determined by ion chromatography ( D I O N E X system 14) and NH4-N was analyzed by Bremners' method (Bremner and Keeney, 1965). TN and TP was measured by flow injection analysis (Haga et al., 1988) based on the persulfate digestion method
Table 2. The mean (.~) and SD of the treatment data in the experiment
Effluent NLAP
IAP-1.0
IAP-3.5
Influent (rag I-i)
(rag I- t) .~ SD
Removal*
(rag I i) g SD
Removal*
I
TOC Total N Total P
552 276 160
25.7 + 1.5 114.4 + 13.6 83.5 + 16.1
95.3% 58.6% 47.6%
26.5 + 0.4 8,5 + 8.5 30,7 _+ 1.6
95.2% 96.9% 80.8%
33.9 + 3.3 24.4 _+22.6 31.1 -+ 1.4
93.9% 91.2% 80.6%
2
TOC Total N Total P
828 414 240
36.5 + 5.7 157.7 + 8.8 116.4_+7.6
95.6% 61.9% 51.1%
35.4 _+6,7 8,4 _+2.7 21,3_+ 6.9
95.7% 98.0% 91.1%
39.6 + 6.6 14.6 _+8.0 27.6_+8.7
95.3% 96,5% 88.5%
3
TOC Total N Total P
690 465 127
75.9 _+8.5 236.0 _+ 10.0 131.5 -+ 18.4
89.0% 49.2% --
54,0 _+ 1.8 21,0 _+7.1 63,8 -+ 6.1
92.1% 95.5% 49.8%
No experiment
4
TOC Total N Total P
664 674 79
64.4 _+4.5 504.0 _+ 1.2 82.9_+2.5
90.3% 25.2% --
56,2 _+3.5 187.5 _+ 19.9 64.3_+8.5
91.5% 72.2% 18.6%
53.8 _+0.5 91.9% 192.4 _+6.4 71.5% 63.3_+10.0 19.9%
Run Items
*Removal efflciencies in the tables were calculated as: total E removal (%) = ~ x 100. Total h total amount of pollutant in daily influent. Total E: total amount of pollutant in daily effluent.
0.45 0.05
(rag I ') £ SD
Removal*
1379
Nutrient removal in activated sludge units
Time 0 2 4 6 8 I0 12 14 16 18 202224(0)
N Sedimentn L Discharge A Chorge P Aeration t Sedimentnj A Discharge
~I
IPo Charge
Aerotior, ~ ~ ~ m ~] ~ ~ ~ ~I
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I ~
~
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(Langner and Hcndrix, 1982). A scmi-micro-Kjeldahl method was applied of the original wastewater to detect deterioration during stock periods. SS, MLSS and MLVSS was measured weekly. All analyses made were in accordance with the procedures of APHA (1985). In the time course of each treatment, pH, DO, TOC, TN, NH4-N, NO2-N, NO3-N, TP and PO4-P was measured to follow the reduction process for nitrogen and phosphorus. Samples were centrifuged at 3000 rpm for 5 rain and the supernatant samples were subjected to the analyses. MLSS, MLVSS and TN and TP of activated sludge were determined just before and after the time course measurements.
RESULTS AND DISCUSSION Two types of data were obtained. The first was the set of routine data from samples collected from each unit two or three times a week at steady-state operation. These data defined the average performance of each unit based on the concentrations of the pollutants in the influent and effluent. The other data were collected along the time course of treatments on the last day of the collection period of the above sample. The time course profile was obtained to find the effect
£ ioI (a)
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Fig. 2. Comparison of the NLAP and IAP-I.0 operations in Run 1 (BOD loading = 0.50 kg m -3 d-~; N/BOD = 0.18). (a) Changes of pH, DO and TOC with the NLAP. (b) Changes of nitrogen with the NLAP. (c) Changes of pH, DO and TOC with the IAP-I.0. (d) Changes of nitrogen with the IAP-I.0.
Nutrient removal in activated sludge units of the appropriate aeration and non-aeration periods on the treatment. Percent settled sludge volumes after 2 h sedimentation were kept below 40% at a MLSS concentration of 8500-9000 mg l -~ (Runs l, 3 and 4) and 60% at a MLSS concentration of 13,000-14,000mg 1-1 (Run 2) for all units. Each unit of Runs l, 2, 3 and 4 was operated at sludge ages of 17.5, 17.9, 17.7 and 18.9 days, respectively. The sludge retention time (SRT) of all the units was consequently almost 30 days. In this experiment, little difference was observed between IAP-1.0 and IAP-3.5 for the treatment results. So, we hereafter regarded IAP-I.0 as a representative IAP.
1381
BOD, TOC and SS removals High removal efficiencies (89.0-99.5%) for BOD, TOC and SS were attained with both IAP and NLAP in all runs. TOC of the effluent is shown in Table 2. High MLSS concentrations in the units may explain the above performances. In fact, the food-tomicrooganism ratio (F/M) in those units was low (0.054-0.059 g BODs (g MLSS)-~). TOC concentration profiles for each unit are presented in Figs 2, 3, 4 and 5. TOC reduction occurred immediately after the aeration in all runs and the reduction was observed even at the first non-aeration period in the IAP. At the earlier stage of the non-aeration period in the IAP operation, a little increase of
NLAP
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1382
TAKASHIOSADAet al.
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Fig. 3. Comparison of the NLAP and IAP-1.0 operations in Run 3 (BOD loading =0.50kg m -~ d t; N/BOD = 0.31). (a) Changes of pH, DO and TOC with the NLAP. (b) Changes of nitrogen with the NLAP. (c) Changes of pH, DO and TOC with the IAP-I.0. (d) Changes of nitrogen with the IAP-I.0. TOC concentration appeared especially in Run 2 [Fig. 5(a)]. No difference was found between Run 1 (BOD 0.50 kg m -3 d -1) and Run 2 (BOD 0.75 kg m -3 d -a) for BOD, TOC and SS removal etticiencies. Those removal efficiencies at BOD 0.50 kg m -3 d loading were slightly affected by increasing the N/BOD ratio of the influent. Nitrogen removal
Large differences in the removal of nitrogen were observed between IAP and NLAP (Table 2). Removal efficiencies of the lAP (71.5-98.0"/o) were much higher than that of the NLAP (25.2-61.9%). Figure 2(a) and (b) shows the profiles of pH, DO and TOC and nitrogen in Run 1 of NLAP. Though
organic nitrogen and NH4-N in influent were readily oxidized, a noticeable decrease of total nitrogen during the NLAP operation did not occur. When the N/BOD ratio of influent was increased to 0.31, NH4-N was not readily oxidized, due to the accumulation of NOx-N and the concomitant drop in pH [Fig. 3(a) and (b)]. Some organisms are reported to undergo a single stage nitrification-denitrification (aerobic-anoxic) in which organic material in the influent is utilized as the electron donor for the denitrification reaction (Applegate et al., 1980; Kakiichi et al., 1988), however, these authors did not envisage the above problem, because the N/BOD ratio of the influent used was relatively low (0.10-0.12). The incorporation of
Nutrient removal in activated sludge units
1383
IAP-I.O
(o) A m
io
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o
!
0
2
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'~
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16
18
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200 I
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~
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~ ~ . ~ , , "'--,2
.-N
NO3-N A
0
2
4
6
8
I0 12 14 Time in hours
16
18
20
-
-
22
Fig. 4. Changes of (a) pH, DO and TOC, and Co)nitrogen during the IAP-1.0 operation in Run 4 (BOD loading = 0.50 kg m -3 d-I; N/BOD = 0.45). the intermittent non-aeration period in the IAP avoided the accumulation of NOx-N to attain high nitrogen removal in all runs. Extremely high removal (95% above) was achieved with the IAP-I.0 (especially in Runs 1, 2 and 3). Figures 2(d) and 3(d) show the nitrogen profle with the IAP-1.0 in Runs 1 and 3, respectively. NOx-N produced during an aeration period was immediately reduced in the subsequent non-aeration period to nitrogen gas, and nitrification in the aeration periods occurred smoothly [Figs 2(d) and 3(d)] under the stable pH conditions [Figs 2(c) and 3(c)]. Thus, along with the proceeding NH4-N oxidation, total nitrogen and NO~-N decreased in the lAP operation. Warner et al. (1986) reported on the application of the general kinetic model for denitrification in anoxic-aerobic digestion of excess sludge wasted
from the activated sludge process. They described that the stability of alkalinity and pH is a major advantage over purely aerobic digestion. Our results on the animal wastewater show the same advantage over nitrification and denitrification [Figs 2(c) and 3(c)]. Denitrification occurs in anoxic conditions with the existence of organic matter as electron donor. Methanol added to and/or organic matter contained in the influenthave been used for this objective.Thus, in the case of the IAP, denitrification might occur mainly at the earlierstage of the non-aeration period in the operation when organic material in the influent stillremains in the mixed liquor. However, our results showed that denitrificationoccurred mainly after the T O C profilehad already reached steady-state at a low level of T O C concantration [Figs 2(c), 2(d), 3(c), 3(d)
1384
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- I0-12 14 16 18 20-22 T i m e in h o u r s Fig. 5. Changes of (a) pH, DO and TOC, and (b) nitrogen during the IAP-1.0 operation in Run 2 (BOD loading = 035 kg m -3 d-t; N/BOD = 0.18).
and 5]. It suggests that TOC is removed from mixed liquor by adsorption on the surface of the activated sludge or its reservoir in microbial cells and the TOC is then used again for denitrification. Further study is needed to clarify the mechanisms of such denitrification at low TOC. Wiiderer et al. (1987) observed the difference in microbial nitrite reduction rates in the presence of glucose or acetate during anoxic conditions. Investigation of organic matters in wastewater is necessary to assess the limitation for nitrogen removal without any supplemental carbon source. At Run 2, under 0.75 kg m -3 d - t of BOD loading, nitrogen was mainly decreased during the aeration period in the early stage of the lAP operation when the DO stayed at a low level [Fig. 5(b)]. Applegate et al. (1980) assumed that most of the denitrification occurred in the first two channels under low oxygen concentrations (DO 0.1-0.9 ml 1-l) in a multi-channel
oxidation ditch system. What types of nitrogenous gases were released during the denitrification process remains unsolved. Phosphorus removal
Removal efliciencies for phosphorus with the lAP were higher than those with the NLAP (Table 2). A high rate of removal of 91% was achieved in Run 2 and we confirmed that the removal phenomenon was composed of the release of phosphorus during the non-aeration periods and of the excess uptake of phosphorus in the aeration periods [Fig. 6(b)], however, this was not clear with N L A P [Fig. 6(a)]. A similar phenomenon has been reported by Levin et al, (1965) and Shapiro et aL (1967). Accumulation of phosphorus in activated sludge was observed in the lAP. Excess sludge on the last day in Run 2 contained 6.5% of phosphorus on a dry matter basis, which was
Nutrient removal in activated sludge units higher than that of the NLAP (4.3%). Gradual increase of phosphorus in the water treated by the NLAP [Fig. 6(a) and (c)] seemed to result from the release of phosphorus from activated sludge. At Run 4, the phosphorus profile during IAP-1.0 operation showed the same tendency as that of the NLAP operation [Fig. 6(c) and (d)].
1385
mated to be 0.2-0.4 (Haga et aL, 1989), the application of the IAP for swine wastewater treatment might anticipate the removal of nitrogen to satisfy the effluent standards. When the N/BOD ratio of the influent increased to 0.31 (Run 3) and 0.45 (Run 4), phosphorus removal efflciencies with the IAP-1.0 decreased to 49.8 and 18.9%, respectively (Fig. 7), though the P/BOD ratio of the influent was lower (Table 1). Barnard (1976) reported that the presence of NO~-N disturbed the release of phosphorus during the non-aeration period, as did the presence of molecular oxygen, and diminished the uptake of phosphorus during the aeration period. In our experiments, those disturb ances were observed with the NOx-N concentration not only in Run 4, but in Run 3. In order to achieve
N/BOD ratio and the removal of nitrogen and phosphorus The relationship between the N/BOD ratio of the wastewater and the removal of nitrogen and phosphorus is summarized in Fig. 7. Nitrogen removal efficiencies were nearly constant up to an N/BOD ratio of 0.31, and decreased with an increase in the ratio. As the N/BOD of swine wastewater was esti-
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a higher removal for phosphorus it is essential to attain almost complete removal of nitrogen by a single-sludge system such as the lAP. At the end of the aeration period, nitrogen was mainly detected as NO 2-N with the lAP operation in Run 3 at a higher N/BOD ratio (0.31), though both NO 2-N and NO~-N were found in Run 1 at a lower N/BOD ratio (0.18) [Figs 2(d) and 3(d)]. Turk et al. (1989) reported on the advantage of the shortened pathway that bypassed the nitrite oxidation step to nitrate and the subsequent nitrate reduction step to nitrite by free-ammonia (NH3). The most remarkable advantage may be the high nitrogen removal via the intermediary nitrites (NO2-N). However, when the N/BOD ratio of the influent in the IAP-1.0 was as high as 0.45, the nitrogen removal efficiency decreased to approx. 72% (Table 2). NOx-N, which built up during the aeration period, was partly
reduced to nitrogen gas at the next non-aeration period [Fig. 4(a)]. As a result, NO2-N accumulation occurred and the pH of the unit declined to 6.3 [Fig. 4(b)]. Feasibility o f the l A P .[or swine farms
The fill-and-draw type activated sludge system is widely used in swine farms which have only a limited area in the suburbs. The operational conditions for these experiments were mostly the same as the actual one; for example, once-a-day charge and discharge, 3 days of HRT and the characteristics of the influent (Haga et al., 1989). Taking into account the economical aeration and ease of application (just changing the aeration program with a timer) on the lAP, this system will provide a promising means for nitrogen and phosphorus control in animal wastewater.
Nutrient removal in activated sludge units
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Acknowledgements--The authors would like to thank Dr H. Tanaka for helpful comment on and critical reading of the manuscript, and Drs H. Mayumi, M. Kawaguchi and M. Yonaga for stimulating discussion, all of National Institute of Animal Industry, Japan. This work was supported in part by the Project "Research and Development on the Techniques for the Removal of Nitrogen and Phosphorus from Livestock Wastewater" (FY1984-1988), Environment Agency, Government of Japan, for which the authors express their thanks.
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REFERENCES
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N / B O D Ratio Fig. 7. Effect of the N/BOD ratio of the influent wastewater on the removal efficiencyof nitrogen and phosphorus with the NLAP and IAP-1.0 treatments under 0.50 kg m -3 d -~ BOD loading. - - O - - , N removal with the IAP-1.0; - - I - - , N removal with the NLAP; ---C)---, P removal with the IAP-I.0, ---[]---, P removal with the NLAP. CONCLUSIONS The experiments in a fill-and-draw type activated sludge unit in a single tank system have been performed with both the IAP and NLAP operations on some typical wastewater prepared from swine feces and urine. The following results were obtained. (1) BOD, TOC and SS removal efficiencies with the lAP operation were as high as those with the NLAP for all wastewater used, though the total aeration period in the lAP were nearly half of that of the NLAP. (2) In the removal of nitrogen and phosphorus, large differences between the lAP and NLAP were observed under a BOD loading of 0.50kg m -3 d -l without any supplemented carbon sources and pH stabilizers. (a) At an influent N/BOD ratio of 0.18, removal efficiencies for total nitrogen in the IAP-1.0 and NLAP were 96.9 and 58.6%, and for total phosphorus were 80.8 and 47.8%, respectively. Along with NH4-N oxidation (aeration periods), total nitrogen and NOx-N decreased in the lAP operation. As a result, extremely high nitrogen removal by the lAP was accomplished. Under these conditions, phosphorus removal occurred with the release of phosphorus during the non-aeration periods followed by the excess uptake of phosphorus during the aeration periods in the activated sludge. (b) At a higher influent N/BOD ratio of 0.31, the removal efficiency for total nitrogen in the IAP-I.0 was 95.5%, but that for phosphorus was 49.8%. (c) At an even higher influent N/BOD ratio of 0,45, removal efficiencies for nitrogen and phosphorus in the IAP-I.0 were 72.2 and 18.6%, respectively.
APHA (1985) Standard Methods for the Examination o f Water and Wastewater, 16th edition. American Public Health Association, Washington, D.C. Applegate C. S., Wilder B. and DeShaw J. R. (1980) Total nitrogen removal in a multi-channel oxidation system. J. Wat. Pollut. Control Fed. 52, 568-577. Barnard J. L. (1976) A review of biological phosphorus removal in the activated sludge process. Water Sth Afr. 2, 136-144. Bremner J. M. and Keeney D. R. (1965) Steam distillation methods for determination of ammonium, nitrate and nitrite. Analyt. chim. Aeta 32, 485-495. Chayovan S., Gerrish J. B. and Eastman J. A. (1988) Biogas production from dairy manure: the effect of temperature pertubation. Biol. Wastes 25, 1-16. Chen T. H., Day D. L. and Steinberg M. P. (1988) Methane production from fresh versus dry dairy manure. Biol. Waste 24, 297-306. Haga K. Osada T. and Harada Y. (1988) Flow injection analysis for the determination of total nitrogen and total phosphorus in animal wastewater. J. Jpn. Swge Wks Assoc. 25(286), 74-80 (in Japanese). Haga K., Osada T. and Harada Y. (1989) Characterization of piggery wastewater and the control of nitrogen and phosphorus. Envir. Inform. Sei. 18, 57q50 (in Japanese). Honda K. (1974) Treatment of the wastewater from animal housing by the oxidation ditch system. Technical Report No. 3 (Research Council Secretariat), Ministry of Agriculture, Forestry and Fisheries (in Japanese). Honda A., Ito H. and Kawakita T. (1974) Swine waste treatment by worm through medium board. J. Wat. Waste 16, 1129-1140 (in Japanese). Kakiichi N., Kamata S, lto O., Yamano S. and Uchida K. (1988) Relationship between gentle stirring time and simultaneous removal of nitrogen and phosphorus from swine wastewater by modified aerated lagoon process. Jpn. J. Zooteehnol. Sei. 59, 1027-1033. Kameoka T., Kagi T., Sakimoto M. and Inno Y. (1986) Characteristics of concentrated wastewater treatment of swine by the rotating disc system. Jpn. J. Zooteehnol. Sei. 57, 209-215 (in Japanese). Langner C. L. and Hendrix P. F. (1982) Evaluation of a persulfate digestion method for particulate nitrogen and phosphorus. Wat. Res. 16, 1451-1454. Levin G. V. and Shapiro J. (1965) Metabolic uptake of phosphorus by wastewater organisms. J. Wat. Pollut. Control Fed. 37, 800-821. Ng W. J. and Chin K. K. (1988) Treatment of piggery wastewater by expanded-bed anaerobic filters. Biol. Waste 26, 215-228. de la Noue J. and Basseres A. (1989) Biotreatment of anaerobically digested swine manure with microalgae. Biol. Waste 29, 17-31. Osada T., Haga K. and Harada Y. (1989) Removal of nitrogen from swine wastewater by limited aeration process. Jpn. J. Wat. Pollut. Res. 12, 122-130 (in Japanese). Safley L. M. Jr and Westerman P. W. (1989) Anaerobic lagoon biogas recovery systems. Biol. Waste 27, 43~52.
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Shapiro J., Levin G. V. and Humberto Z. G. (1967) Anoxically induced release of phosphorus in wastewater treatment. J. War. Pollut. Control Fed. 39, 1810-1818. Sheath R. W. (1988) The effect of removing solids from aerobically treated piggery slurry on the VFA levels during storge. Biol. Waste 26, 175--188. Svoboda I. F. and Fallowfield H. J. (1989) An aerobic piggery slurry treatment system with integrated heat recovery and high-rate algal ponds. War. Sci. Technol. 21, 277-287.
Turk O. and Mavinic D. S. (1989) Stability of nitrogen build-up in an activated sludge system. J. Wat. Pollut. Control Fed. 61, 1440-1448. Warner A. P. C., Ekama G. A. and Marais G. V. R. (1986) The activated sludge process--4, application of the general kinetic model to anoxic-aerobic digestion of waste activated sludge. Wat. Res. 20, 943-958. Wilderer P. A., Jones W. L. and Dau U. (1987) Competition in denitrification systems affecting reduction rate and accumulation of nitrogen. Wat. Res. 21, 239-245.