NUTRIENT REMOVAL FROM SECONDARY EFFLUENT BY SOIL

Transcription

1 NUTRIENT REMOVAL FROM SECONARY EFFLUENT BY SOIL K. V. L1 and J. T. Claytn 1Bi-Resurces Engineering epartment, Nva Sctia Technical Cllege, Halifax, N.S. BJ X4, and1 Fd and Agricultural Engineering epartment, University f Massachusetts, Amherst, Mass. 1 Received 1 February 1978 L, K.V. and J.T. Claytn Nutrient remval frm secndary effluent by sil. Can. Agric. Eng. : Sil clumns were used t study the effects feffluent applicatin rate and applicatin frequency n wastewater renvatin thrugh sil media. Attempts were made t determine the feasibile wastewater lading rate. Chemical analyses were perfrmed n sil, wastewater and filtrate samples. Bench tests were cnducted t determine the nutrient adsrptive prperties fa selected sil. Under equilibrium batch cnditins, ammnia adsrptin n Ninigrit sandy lam can be expressed by the Freundlich adsrptin istherm. In the ph ranges fr usual wastewaters, arund 7., nitrate adsrptin n sil was insignificant. Clumn test results shwed that all sil clumns achieved 99% r greater phsphate remval. At the end fthe 1-wk test perid, nitrgen cncentratins in all the filtrates were belw the Canadian drinking water standard f 1 ppm N-N. Test results als shwed that denitrificatin culd have been a significant factr in nitrgen remval. INTROUCTION Althugh land applicatin fwastewater is an ld practice, it is nly recently that it has received widespread interest f a scientific nature (Parizek et al. 1967; Pund and Crites 197). In land applicatin f wastewater, large quantities f suspended and disslved materials are applied t a sil surface. Part f these materials may be temprarily r permanently retained in the rt zne; the remainder will be carried undergrund by the flwing water. In rder t develp ptimum management schemes fr envirnmental cntrl, particularly the preventin f sil and water pllutin, it is imprtant t investigate the prcesses that cntrl wastewater mvement frm the sil surface thrugh the rt zne and n dwn t the grundwater table. There is clearly a lack f basic infrmatin n the effluent applicatin rate, the maximum lading, the frequency f applicatin fr varius types f sil, and the effects fwastewater effluent n sil prperties, grundwater qualities, crps, animals and human beings. In this study, experiments were cnducted with the fllwing bjectives: 1. T measure the nutrient adsrptive prperties f a selected sil;. T study the effects f effluent applica tin rate and applicatin frequency n wastewater renvatin thrugh sil media;. T determine the feasible wastewater applicatin rates n the sil-water system. EXPERIMENTAL PROCEURE Bench Tests Bench tests were cnducted t determine the nutrient adsrptive prperties f Ninigrit sandy lam. The prcedure used was adapted frm Preul and Schrepfer (1968). Three series f tests were cnducted in which fixed weights f sil were allwed t equilibrate with slutins f graded cncentratins f NH-N, N-N, and phsphate, respectively, fr perids f - days. The nutrient adsrptive capacities ) 1 Q. CC O C/> Q < "1 I I I I I I I \ I I I II q. = 1. C 1 j i i Mini i i i were then determined based n the riginal cncentratins in the sil and the final cncentratins in the slutins. In the case f nitrate nitrgen adsrptin, tw series f tests were run t bserve the effect fph n N-N adsrptin. In the first series, theph was nt adjusted. In the secnd series, the ph was adjusted t SOLUTION CONCENTRATION (C in mg/ ) Figure 1. Adsrptin istherm fr NH-N. Clumn Tests Clumn tests can prvide infrmatin clsely related t practical cnditins. Atthe same time, cmplicated cnditins can be simplified. A tw-way classificatin experiment was designed t investigate the effects f interactins between wastewater applicatin rate and applicatin frequency n effluent renvatin. After a thrugh review f current literature, three wastewater applicatin rates (, 1 and cm/wk), and tw applicatin frequencies (daily and weekly) were chsen. Three testing perids (4, 8 and 1 wk) were selected. ith these variables cnsidered, 18 sil clumns were cnstructed and tested. The clumns were made f plexiglass, 1.7 cm thick. The crss-sectinal 1 dimensins feach clumn were 1X1 cm. Bth Ninigrit sandy lam and Hinckley sand were air-dried and then passed thrugh a standard N. 1 sieve befre being placed in the clumns. In rder t achieve relatively hmgeneus and repeatable sil cnditins, empty clumns were placed n a shaker, and the sils were pured thrugh a funnel int the clumns. Fr each clumn, the bttm 1 cm was filled with Hinckley sand and then Ninigrit sandy lam was cmpacted t a depth f 4 cm. This was t simulate a field cnditin, with a sand layer lying 4 cm belw the sil surface. Secndary effluent frm the estfield astewater Treatment Plant, estfield, Massachusetts, was used fr this experiment. The secndary effluent feed applicatin rate was cntrlled by a regulating valve. Fr each applicatin, the valve was frequently adjusted s that the sil surface was saturated, but nt flded, since under field cnditins surface runff shuld be prevented. Plyethylene cvers were used n all sil clumns t prevent evapratin. All tests were cnducted at a temperature f 1 C in rder t mre clsely simulate subsil cnditins and t eliminate the effect 64 CANAIAN AGRICULTURAL ENGINEERING, VOL. NO.l, JUNE 1978

2 E 1.6 IK _ f temperature variatins. uring the testing perid, effluent was cllected daily frm the bttm f each clumn. This effluent was then analyzed fr ttal rganic carbn (TOC), ttal N, NH-N, N-N, rganic N and ttal P (Taras et al. 1971). In rder t find ut the vertical distributin prfile f nitrgen and phsphate in the sil, the sil clumns were sectined int.-cm increments and analyzed fr N (all frms) and P after each testing perid. RESULTS AN ISCUSSION z Q. CC O ) Q < 4 66C 16 8C Bench Tests Ammnia nitrgen adsrptin Ammnia nitrgren adsrptin data are presented in Fig. 1. They fllw the Freundlich istherm (eber 197) i In Qe - KC (1) 1. i 1 1 SOLUTION CONCENTRATION (C in mg/l ) Figure. Phsphate adsrptin istherm. where qe is the adsprtin f NH-N in micrgrams per gram f dry sil, C is the cncentratin f NH-N in the slutin when equilibrium is reached, and, K and n are empirical cnstants. hen lg qe is pltted against lg C, a straight line with slpe 1In is btained. Fr this case, n = 1.94 and K = 1.. TABLE I. NITRATE SOIL ASORPTION ON TABLE HI. AVERAGE EFFLUENT QUALITY FROM COLUMNS HAVING cm/wk APPLICATION RATE Initial N-N ph Final NO-N Adsrptin f NO-N (Mg/g) Testing perid aily r weekly Ttal N (mg/l) Organic N NO-N N-N Ttal P Ttal rganic carbn f TABLE II. AVERAGE CHARACTERISTICS OF SECONARY EFFLUENT ph Nitrgen Phsphrus Ttal rganic carbn Ttal N NH-N Organic-N NO-N N-N Ttal P mg//.41 mg//(asn) 1.mg//(asN).9 mg//(as N).1 mg//(asn) 1.84 mg//.18 mg// t means nt applicable, since there was n effluent. CANAIAN AGRICULTURAL ENGINEERING, VOL. NO.l, JUNE

3 TABLE IV. AVERAGE EFFLUENT QUALITY FROM COLUMNS HAVING 1 cm/wk APPLICATION RATE aily Ttal rganic Testing r Ttal N NH-N Organic N N-N N-N Ttal P carbn perid weekly f f means nt applicable, since there was n effluent. Nitrate nitrgen adsrptin Nitrate nitrgen adsrptin data are shwn in Table I. The results indicate that the adsrptin f NO-N is strngly dependent n/?h. In the first series ftests, the final ph was abut.7 and significant adsrptin f NO-N ccurred. In the secnd series f tests, the finalph was abut 7. and n significant adsrptin f NO-N resulted. It can be seen that the adsrptin f NO-N under cnditins cmmnly fund in grundwater r secndary effluent with a ph arund 7. shuld nt be significant. Hwever, it can be significant ifph is belw 6.. Phsphate adsrptin Phsphate adsrptin data are presented in Fig.. The data can be fitted int the Langmuir istherm (eber 197): Qe= where QTbc 1+ be () Qe = the amunt fphsphate adsrbed per unit weight f dry sil, Q = theamunt f phsphate adsrbed per unit weight f sil in frming a cmplete mnlayer n the surface, b - cnstant, c = cncentratin in slutin at equili brium. Fr this case, b and Q - 1. mg/g. Clumn Tests astewater characteristics At the beginning f the tests, abut / f secndary effluent were taken frm the estfield astewater Treatment Plant, estfield, Massachusetts and then stred at a temperature f 4 C. Ttal phsphate, nitrgen and ttal rganic carbn (TOC) analyses were dne weekly. Test data shwed very little variatin in ttal P, N and TOC thrughut the strage perid. The average values are given in Table II. Sil clumn effluent quality The effluent frm sil clumns was cllected daily and stred at 4 C. Chemical analyses were dne weekly. The results are given in Tables III, IV and V. Generally, the ph values were arund 7.. Frm these data, it can be seen that TOC in the effluent decreased with time. Hwever, the values were higher than thse f the secndary effluent. It is believed that rganic carbn was gradually leached ut f the sil clumns. Ttal P in the effluent was in the range f -. mg//. The average value fr all the samples was.1 mg//. Therefre, the phsphate remval efficiency f all the sil clumns was at least 99%. Nitrate cntents were very high during the first wk after effluents started draining frm the clumns. There are tw pssible explanatins: (1) Since the sils were air-dried, the micr-rganism ppulatin shuld have been very lw when the test was started. Therefre, a perid f abut wk might have been required fr micr bial grwth t reach maturity. The high nitrate cncentratin might have been due t leaching f nitrate riginally in the sil. () It is very pssible that nitrificatin ccurred and was a dminant factr fr the first 1 r wk. Nitrate cncentratin in the effluent frm all the clumns shwed a decreasing trend with time. Hwever, the clumns having the cm/wk applicatin rate shwed a slight increase in the last 4 wk. The rapid decrease in nitrate cncentratin and the slight variatin in rganic-n cncentratin were interpreted as evidence f denitrificatin. As far as nitrate cncentratin is cncerned, this suggests that denitrificatin may be an imprtant factr in wastewater renvatin. It is bvius that NH-N cncentratin in the effluent increased with time. The pssible chemical reactins invlved may be hypthesized, e.g. mineralizatin f rganic nitrgen, and nitrate reductin, but cannt be verified by the results f this study. In Fig., the variatins f the ttal nitrgen cncentratin in the weekly cllected effluents are presented. The average ttal nitrgen cncentratins are pltted against time. It is clear that during the first wk after drainage started, the nitrgen cncentratin in the effluent frm all the clumns shwed a decreasing trend with time. This was fllwed by fluctuatins and a later slw increase with time. By the end f the 1-wk testing perid, effluent frm the clumns with cm/wk applicatin rate had the lwest ttal nitrgen cncentra tins. Effluent frm the clumns with 1 and cm/wk rates had slightly higher ttal nitrgen cncentratins, ranging frm 6.4 t 9. mg//. This trend f nitrgen cntents increasing with time may well have been due t a nitrate applicatin rate that was higher than the rates f denitrificatin and nitrate reductin. It culd als have been due t a slwdwn in denitrificatin as rganic carbn was gradually leached ut f the clumn. Further studies are needed t cnfirm r deny this. hen drainage first started, the nitrgen cntent (mstly nitrate) was high. Hwever, it can be seen that the lwer the wastewater ladings, the higher were the nitrgen 66 CANAIAN AGRICULTURAL ENGINEERING, VOL. NO.l, JUNE 1978

4 cntents in the effluents cllected. It is bvius that there was a dilutin effect. Fr the cm/wk applicatin, less wastewater was applied. Therefre, nitrate leaching resulted in the highest nitrgen cncentratin in these effluents as cmpared with the 1 and cm/wk applicatins. Fr the 1cm/wk applicatin, it is nted that n the rd wk f the testing perid, the effluent nitrgen cncentratins were already belw thse fthe input wastewater. This means that micr-rganisms in the sil TABLE V. AVERAGE EFFLUENT QUALITY FROM COLUMNS HAVING cm/wk APPLICATION RATE aily Ttal rganic Testing r Ttal N NH-N Organic N N-N N-N Ttal P carbn perid weekly f f means nt applicable, since there was n effluent. became active within - wk. Under field cnditins, this kind f leaching may r may nt happen. Sils are usually mist and the sil micrbial ppulatin will always exceed that fan airdried sil. Therefre, it may be expected that nitrate leaching will nt ccur at the beginning f wastewater applicatin. Hwever, this can nly be cnfirmed by ding field plt tests. Based n the effluent nitrgen cncentratins, nitrgen remval efficiencies f clumns with different applicatin rates and applicatin frequencies are given in Table VI. It can be seen that the nitrgen remval efficiency decreased with increasing lading rate. At the end f a 1-wk perid, the clumns with the cm/wk applicatin rate had the best nitrgen remval efficiency. In bth the cm/wk and the cm/wk series, effluent applied weekly had a better renvatin effect than that applied daily. This may have been due t a lnger resting perid fr weekly applicatin. Fr the 1 cm/wk series, the fact that daily applicatin achieved better nitrgen remval than that f weekly applicatin cannt be explained. It might have resulted frm sample variatin. Hwever, this culd nt be verified as n replicates were available fr the last 4 wk. Fr the 1 cm/wk and cm/wk applicatin rates, the remval efficiency increased in the first few weeks and then decreased t arund 6-74%. The increase f remval efficiency might have been due t sil micrbes that were gradually reaching maturity. The decrease culd have been due t a slwdwn in denitrificatin and nitrate reductin as rganic carbn was gradually leached ut fthe clumns, r it may simply have been due t nitrate lading rates that were higher than the rates f denitrificatin and nitrate reductin. TABLE VI. NITROGEN REMOVAL EFFICIENCY Applicatin rate Time (week) cm/wk 1 cm/wk cm/wk aily eekly aily eekly aily eekly %(4) -98.7%(4) %() %().9%(6).%(6) 4-1,.% -9.7%(4) 9.9, (4) 81.7%(8) 7.9%(8) -4.7% 7.4%() 77.96%() 79.1%(1) 78.18%(1) 6-6.1%(): :.8%() 8.4%(6) 77.%(6) 8.8%(1) 7.8%(1) % 8.98% 8.16% 78.64% 76.99% 81.64% 8 1.6%(4) 8.7%(4) 8.66%(8) 71.7%(8) 8.4% 7.86% % 8.6% 8.8% 76.86% 74.% 77.7% %() 84.8%() 81.6%(1) 74.%(1) 66.6% 71.91% % 8.48% 69.% 7.% 61.% 69.8% %(6) 8.%(6) 7.79%(1) 6.7%(1) 64.9% 71.98% t means nt applicable. {Number in parentheses stands fr equivalent ttal wastewater lading; i.e. cm/wk fr 1 wk is equivalent t 1 cm/wk fr wk. CANAIAN AGRICULTURAL ENGINEERING, VOL. NO.l, JUNE

5 The remval efficiency might have been reduced ifthe tests were allwed t cntinue. Hwever, the data shwed that even withut crp uptake, remval efficiencies f6-8% can be maintained fr different applicatin rates. It is expected that if suitable crps were incrprated int the system, the remval efficiency wuld increase. As shwn in the last line ftable VI, the nitrgen remval efficiency with different wastewater applicatin rates varied by \ E z 1 "i i r abut 1-%, while the amunt f wastewater applied varied tw t fur times. Therefre, a cmprmise between the nitrgen remval efficiency and the rate f lading will have t be cnsidered. The final decisin prbably will be ne based n ecnmics. In this study, the influential factrs were cntrlled under labratry cnditins; therefre the results may nt be directly applicable t the field applicatin f waste effluent. Hwever, these results can be expected t reflect general trends. The variatin f temperature was nt cnsidered. The clumns were packed with 4 cm f tp sil. In the field, the tp sil may nt be as deep and the micrbial ppulatin wuld prbably be different. Mre studies are needed t establish crrelatin between results frm clumn studies and field cnditins. The lading f cm/wk fr 9 wk is equivalent t that f cm/wk fr 6 wk. In the New England area and the Maritime Prvinces, 6 wk shuld cver the spring, summer and autumn seasns, which are suitable fr spray irrigatin. Assuming that the results btained in this study are valid fr field cnditins, ne mayexpect that with an applicatin rate f cm/wk fr 6 wk, the nitrgen remval efficiency wuld be arund 7%. If suitable crps were planted, this remval efficiency wuld be higher (Spper 197). z (J cc < _1 L I _1 L _L J_ J L TIME (EEK) Figure. Ttal nitrgen cncentratin vs. time. TABLE VII. PHOSPHATE PROFILES AT THE EN OF THE 1-wk PERIO (IN mg P/g RY SOIL) Applicatin rate cm/wk 1 cmi/wk cm/wk epth aily eekly aily eekly aily eekly (cm) t fsample was nt taken at this depth. Nutrient distributin in sil clumns At the end f each testing perid, clumns were sectined int.-cm increments and analyzed fr nitrgen and phsphate. Phsphate prfiles at the end f a 1-wk perid are given in Table VII. Since it was bserved, hwever, that phsphate accumulated in the tp.- cm f the clumn, nly the prfiles f the tp 1 cm are presented. The averaged value f phsphate riginally present in the Ninigrit sandy lam was 1.1 mg P/g dry sil. It may be seen that the phsphate accumulatin in sil decreased with depth. Fr the case fthe cm/wk applicatin rate, phsphate accumulated in the tp. cm f the sil; it decreased frm 1.6 t 1.4 and 1.66 t 1. mg P/g dry sil fr daily and weekly applicatins, respectively. Fr the 1cm/wk and cm/wk cases, the accumulatin reached a depth f cm; hwever, the P cntent in the sil fr clumns with cm/wk applicatin rate were higher than thse fclumns with 1 cm/wk applicatin rate. The ttal nitrgen in all the clumns appeared quite unifrmly distributed with depth. Hwever, NH-N and N-N were distributed increasingly and decreasingly with depth, respectively. ata fr clumns 17 and 18, at the end fthe 1-wk perid, are given in Table VIII. The interface between sand and sandy lam was at a depth f apprximately 4 cm. It can be seen that bth NH-N and N-N cntents in the Hinckley sand were cnsiderably lwer than thse fthe Ninigrit sand lam. ata fr all the clumns were reprted elsewhere (L 197). Mass balances were perfrmed fr sil clumns n a weekly basis. Since the ttal nitrgen in the sil clumns remained fairly cnstant bth befre and after wastewater applicatin, the nitrgen remval efficiency given in Table 68 CANAIAN AGRICULTURAL ENGINEERING, VOL. NO.l, JUNE 1978

6 TABLE VIII. NH-N AN NO-N + N-N OF THE COLUMNS 17 AN 18 AT THE EN OF THE 1-wk PERIO (UN mg N/RY SOIL) epth NH-N N-N-N NH-N N-N-N (cm) (mg/g) (mg/g) (mg/g) (mg/g) int the systems, nitrgen remval efficiency wuld have been higher. Althugh there are n detailed quantitative data, it is believed that denitrificatin can be an imprtant factr in land dispsal f waste effluent. Ttal nitrgen lss in the sil clumns amunted t abut 6-8% f the nitrgen input thrugh wastewater applicatin. A prtin f this must be due t denitrificatin. Mre research n denitrificatin in sils is recmmended. ACKNOLEGMENTS The authrs acknwledge the financial supprt f this study by the Office f ater Research and Technlgy, U.S. epartment f the Interir. VI als gave a rugh estimate f the percentage f nitrgen lss that ccurred each week. The results f bench tests indicated that with a ph arund 7., the adsrptin f nitrate nitrgen n sil wuld have been insignificant. Therefre, it was suspected that a large prtin f this nitrgen lss culd have been due t denitrificatin. SUMMARY AN CONCLUSIONS Under equilibrium batch cnditins, ammnia adsrptin n Ninigrit very fine sandy lam can be expressed by the Freundlich adsrptin istherm 1In qe=kc (1) with K- 1. and n In the /?H ranges fr usual wastewaters, n significant nitrate adsrptin n sil will ccur. Phsphate adsrptin n Ninigrit sandy lam can be expressed by the Langmuir istherm Qe = Q be 1+ be with Q - 1. mg/g and b () Clumn test results shwed that all sil clumns achieved 99% r greater phsphate remval. Phsphate frm the applied secndary effluent accumulated in the tp.-. cm f the sil clumns, depending n lading. At the end f the 1-wk test perid, clumns with cm/wk applicatin rate had the best nitrgen remval, abut 8%. Clumns with 1 and cm/wks applicatin rates had nitrgen remval ranging frm 6 t 74%. Nitrgen cncentratins in all the effluents were belw the recmmended limit f 1 mg// N-N fr drinking water. It is expected that if crps were incrprated LO, K.V An experimental and simulatin study f waste effluent filtratin thrugh sil. Ph.. issertatin. University f Massa chusetts, Amherst, Mass. PARIZEK, R.R., L.T. KAROS,.E. SOPPER, E.A. MYERS,.E. AVIS, MA. FARREL, and J.B. NESBITT. aste water renvatin and cnservatin. Penn. State Studies N., Pennsylvania State Univer sity, University Park, Pa. POUN, C.E. and R.. CRITES aste water treatment and reuse by land applicatin. Vlumes I and II. Office f Research and evelpment, U.S. Envirnmental Prtectin Agency, ashingtn,.c. 46. PREUL, H.C. and G.J. SCHROEPFER Travel f nitrgen in sils. J. ater Pllut. Cntr. Fed. 4(1) -48. SOPPER,.E Perennial crp selectin and management fr municipal wastewater irrigatin system. Institute fr Research n Land and ater Resurces, Reprint Series N. 4, Pennsylvania State University, University Park, Pa. TARAS, M.J., A.E. GREENBERG, R.. HOAK, and M.C. RAN Standard methds fr the examinatin f water and wastewater. American Public Health Asscia tin, ashingtn,.c. 6. EBER,.J., Jr Physicchemical prcesses fr water quality cntrl. Jhn iley & Sns, Inc. New Yrk, N.Y. CANAIAN AGRICULTURAL ENGINEERING, VOL. NO.l, JUNE