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e Pergamon Wal. Sci. Tech. Vol. 33, No. 10-11, pp. 79-85, 1996.Copyright © 1996 IAWQ. Published by Elsevier Science Ltd

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IMPROVEMENT OF EFFLUENT QUALITYFOR REUSE IN A DAIRY FARM

Mohamed F. Hamoda* and Saed M. AI-Awadi**

* Department o/Civil Engineering, UAE University, P. O. Box 17555, AI-Ain,United Arab Emirates** Environmental Science Program, UAE University, P. O. Box 17555, AI-Ain,United Arab Emirates

ABSTRACT

This study examined the chemical treatment of wastewaters from a dairy farm in order to improve effluentquality and evaluated the reuse of treated effluent in irrigation. An extensive sampling and analysisprogram was conducted over a period of one year to determine wastewater characteristics at the plant. Ithas been found that the wastewater COD, BOD, solids, nitrogen and phosphorus content are relativelyhigh but daily variations in pollution loads are not considerably high. Waste treatment in primary settlingtanks was found to be insufficient since the effluent quality cannot satisfy the requirements set by themunicipal. Experimental results on chemical treatment using alum as a coagulant indicated that thewastewater pollutants could be effectively reduced in order to obtain a good effluent for reuse inirrigation. A wastewater treatment system has been proposed based on the results of the industrial wastesurvey, evaluation of the existing treatment, and analysis of the jar tests on chemical treatment. Theproposed system can be implemented to produce a good quality effluent for beneficial reuse in irrigation offarm land. Copyright © 1996 IAWQ. Published by Elsevier Science Ltd.

KEYWORDS

Alum; dairy farms; effluent quality; irrigation; wastewater treatment; water reuse.

INTRODUCTION

Reuse of treated wastewater effluents in irrigation of agriculture lands is gaining considerable attention inarid and semi-arid regions of the world where fresh water resources are scare. In many countries,domestic wastewater effluents constitute an additional source of water required for land reclamation,landscaping and crop production. On the other hand, wastewater effluents generated by some industries,e.g. the food industry, has a great potential for reuse in irrigation after receiving appropriate treatment. Inparticular, the dairy processing plants and the dairy farms generate considerable quantities of wastewaterthat could be treated and reused at a reasonable cost.

There are several physico-chemical and biological processes that can be used for the treatment of dairyprocessing effluents (OdIum et ai., Schwer and Clausen, 1989; Mann, 1990; Blan and Navia, 1991;Rusten et ai., 1992). However, selection of appropriate treatment techniques to produce good qualityeffluent suitable for reuse in a cost-effective way remains to be made for each particular plant. This studywas conducted in order to evaluate the performance of a wastewater treatment system and determine itsrole in improving effluent quality for reuse in a large dairy farm (AI-Rawabi) in the United Arab Emirates.The application of treated effluent in irrigation of fodder land is examined.

79

Xl) M. F. HAMODA ,wi S. M. AL-AWADI

MATERIALS AND METHODS

Sources of Wastewater

The farm has 2,500 heads of milking cows producing an average of 30,000 lid of fresh milk. Thegenerated milk is transferred to an adjacent processing plant for the production of bottled fresh milk,yogurt, cram and cheese. The premises, which also include buildings for office and accommodation ofstaff and farm workers, occupy a total of 200 hectares of a sparsely developed desert area. There are threemain sources of wastewater contributing a total flow of 900 m3/d. There are: (a) The milking sheds of thefarm (milking parlors), (b) the milk processing plant, and (c) the office and accommodation buildings.

An additional waste stream originates from a reverse osmosis (R.O) treatment unit used for on-sitedesalination of slightly brackish water supply. The wastewater streams are separated. Thus, this studyfocused on the wastewater generated from the milking sheds which, unlike the other wastewater streams,is considered for on-site treatment and reuse in irrigation.

Existing Wastewater Treatment Facilities

The wastewater collected from milking sheds flows into a common sump where it is pumped outautomatically through a float-control, on-off device into two sedimentation tanks-in-series. Those areconcrete rectangular tanks with identical design. Each tank has a surface area of 15.5 m by 6 m with anaverage depth of 2.5 m and operates on a semi-continuous mode since the flow received is intermittentdepending upon the milking schedule. The tank is divided into two chambers A and B.

The raw wastewater flows into chamber "A" of the first tank where initial settling of suspended particlestakes place while lighter solids float forming a scam layer on the water surface. A baffle separating thetwo chambers extends above the water level to retain the floating scum in the first chamber "A" while thewater flows into the second chamber "B" for settling of suspended particles. effluents from chamber "B"of the first sedimentation tank flows into the second tank for further settling of suspended particles. Thefinal effluent is mixed with the reject from the reverse osmosis unit and is pumped out to irrigate Lucernegrass land in the farm premises. The settled solids as well as the scum are discharged as a slurry into aholding tank from which a tank-lorry collects the slurry regularly for of-site disposal.

Experimental Work

The experimental program, which extended for almost one year, included field sampling and analyses ofwastewater effluents to: (a) Examine the wastewater characteristics, (b) evaluate the performance ofsedimentation tanks, and (c) assess current practice of effluent reuse in irrigation. In addition, laboratoryexperiments were conducted on the farm wastewater effluents employing the standard jar test apparatus toexplore the possibility for chemical treatment to improve effluent quality and determine the optimumchemical dosage. Alum was used as a coagulant during the jar test experimentation.

Analytical Techniques

Raw wastewater and treated effluent samples were collected and analysed to determine organic (BOD andCOD), solids (TS, SS, TDS) , nutrients (N03-N, NH3-N, P04-P), pH, alkalinity, inorganic elements(Ca, Mg, Na, K) and salts (CI, S04)' The analytical procedures followed were those outlined in thestandard methods for the examination of water and wastewater (APHA, 1992).

RESULTS AND DISCUSSION

Analyst'! of Raw 'Vastewater

Effluent quality for reuse in a dairy farm 81

The averagt~ characteristics of the raw wastewater generated at the farm are presented in Table 1. Thew~stewat~r contains high concentrations of organics, solid!: and plant nutrients which are contributed by~p111ed ~l1k and cow dung. Its salt content is relatively high since a slightly brackish groundwater supplyIS used In the farm. Moreover, the chemicals used for cleaning purposes also contribute to the salt contentof the wastewater.

TABLE 1. AVERAGE CHARACTERISTICS OF WASTE EFFLUENTS AS COMPAREDTO IRRIGATION WATER QUALITY

Raw Primary Reject Final Effluent Effluent QualityParametera Wastewater Settled from R.O. after Mixing Guidelines for

Effluent Unit with R. O. Reject IrrigationCOD 1541 755 128 480 30-120SS 850 393 <10 290 10-100TDS 2705 2800 3090 3000 750 - 2000Conductivity 4250 4200 ND 4300 3000(umhos/cm)NH3-N 48.5 ND < 0.1 45 1N03-N 2.2 ND ND 2.0 20P04- P 20 ND 0.12 18 23ALK. 348 400 330 370 200-700Cholorides 930 939 ND ND 40-200Sulfates ND 400 ND ND 100-380Calcium ND 69 ND 128 NAMagnesium ND 110 ND 48 NASodium ND 625 ND 430 190-250Potassium ND 73 ND 190 NApH (units) 7.9 8.2 7.8 7.9 6-8

a All values are in mg/L unless otherwise indicatedND = not determined, NA = not available

Statistical analysis of the data obtained indicate that the waste characteristics are not highly variable.Furthermore, a linear relationship was obtained between the COD and BOD values with a correlationcoefficient of 0.991 and an average COD/BOD ratio of 3.0 indicating that the wastewater isbiodegradable. Similarly, the COD and TS showed a linear relationship (Fig. 1) with a correlationcoefficient of 0.912 and COD/TS ratio of 0.85 reflecting the organic nature of the solids. The farmcontributes considerable pollution loads. The population equivalent of the organic pollutants (BOD) load is18,000 persons based on 90 g/d of BOD per person for domestic wastewater (Metcalf & Eddy, 1991).

Analysis of Primary Settled Wastewater

The primary-settled effluent characteristics were determined over a period of almost six months followingcommissioning of the sedimentation tanks as shown in Table 1. The incoming flow passes through agrease trap prior to the sedimentation tanks. Since the tanks operate on a semi-continuous mode, the liquidis retained in the tank for about six hours. This is a relatively long retention period compared to thoseobserved in the primary sedimentation tanks of municipal wastewater treatment plants. Meanwhile, nochemicals are used to assist the removal of fine particles in the sedimentation tank.

The results obtained from the sedimentation tanks show as average of 31 % COD removal, 39% BODremoval and 53 % SS removal. These values are comparable to those reported for primary sedimentationtanks in municipal wastewater treatment plants (Metcalf & Eddy, 1991) operated at shorter detention times(2 - 3 hours) and reflect the colloidal nature of a large portion of the particles present in the dairy

wastewater.

1\1. F. HAMODA and S. M. AL-AWADI

I • BOD ... TS

X2

8000

7000

6000

- 5000:::::::.enE

4000-c0u 3000

2000

1000

00 1000 2000 3000 4000

BOD or TS (mg/I)5000 6000

Figure 1. Relationships Between COD, BOD and TS for the Dairy Farm Wastewater

The overall characteristics of the settled effluent indicate that the waste still carries significant amounts ofpollutants notably SS and organics. The effluent does not conform with the water quality guidelines forreuse in irrigation (Table 1) but its characteristics are similar'to those of raw sewage received in localmunicipal wastewater treatment plants. In other words, the existing sedimentation tanks can be consideredas pretreatment facilities if it is pemlitted by the municipality to discharge the wastewater into sanitarysewers. However, since the wastewater shall be used in irrigation, further treatment is deemed necessary.

Effluent Reuse in Irrigation

The settled effluent is currently used for irrigating Lucerne grass which is a source of foddor for the cowsin the farm. Beneficial rewards are generally expected both financially and environmentally. Cost savingsand resource conservation are imminent.

In an attempt to improve effluent quality at the present time, the settled effluent is mixed with the rejectfrom the reverse osmosis water treatment unit (Table 1) before being used for irrigation. The finalcharacteristics of the effluent after mixing with the R.O. reject do not totally satisfy the irrigation waterquality as given in Table 1. Although the solids, organics and nutrient content of the effluent decreaseddue to dilation with the R.O. reject (i.e. groundwater), the salt concentration increased slightly. Theeffluent has been used continuously for irrigating Lucerne grass. variations in crop production have beenobserved in an experimental plot of 1.5 hectare for seven consecutive harvesting cycles as illustrated inTable 2. It can be seen that the amount of crop decreased due to excessive use of unsuitable effluent. Sincethe effluent characteristics do not comply with the commonly accepted quality of irrigation water, thesettled effluent must receive additional treatment. This may be possible through chemical coagulation withalum.

Effluent quality for reuse in a dairy farm 83

TABLE 2. VARIATION IN CROP PRODUCTION UTILIZING THE SETTLED WASTEWATEREFFLUENT IN IRRIGATION

ConsecutiveHarvesting Cycles

1234567

Chemical Treatment with Alum

Amount of Crop/1.5 Hectare (ton)

87.155.84.54.04.54.5

RemarksGood Quality HarvestGood Quality Harvest

Good to mediumMediumMediumMediumMedium

Chemical treatment using alum, Alz (S04h, as a coagulant included two sets of experiments on rawwastewater and on effluent after primary sedimentation (effluent of the existing facility). Table 3 showsthe average results of the JAR TEST on alum treatment of different wastewater effluents. These results

TABLE 3. RESULTS FROM THE JAR TEST ON WASTEWATER EFFLUENTS

a. Chemical treatment of raw wastewater

Alum Dose NH3-N COD (mg/L) SS (mg/L) P (mg/L)(mg/L)

Control 87.8 1880 320 29.220 mg/L 87.5 1866 300 27.640 mg/L 87.5 1820 280 26.360 mg/L 87.2 1820 270 24.980 mg/L 86.9 1820 260 24.9100 mg/L 84.2 1792 240 22.5

b. Chemical treatment of raw wastewater

Alum Dose NH3-N COD (mg/L) SS (mg/L) P (mg/L)(mg/L)

Control 87.2 1852 320 26.6140 mg/L 81.0 1792 200 16.5160 mg/L 80.8 1792 170 14.4180 mg/L 80.2 1788 175 12.6200 mg/L 80.2 1696 160 11.2220 mg/L 80.0 1696 130 11.5

c. Chemical treatment of primary-setteled wastewater (effluent from existing facilities)

Alum Dose NH3- N COD (mg/L) SS (mg/L) P (mg/L)(mg/L)

28.2Control 178 931 8020 mg/L 164 796 38 26.140 mg/L 156 778 35 23.280 mg/L 146 771 32 21.3120 mg/L 146 768 30 23.2250 mg/L 139 694 28 12.5

f\1. F. HAf\10DA ;U1J S. M. AL-A WADI

d. Chemical treatment of primary-settled wastewater (effluent from existing facilities)

Alum Dose

Control100 mg/L200 mg/L300 mg/L400 mg/L500 mg/L

NH3-N(mg/L)

167159155152149149

COD (mg/L)

774582515501483454

SS (mg/L)

553430262318

P (mg/L)

26.920.014.18.04.53.6

indicate that alum treatment could substantially improve the quality of the effluent from the existingfacilities regarding suspended solids (SS) and phosphorus (P) removal. However, this treatment was notequally effective in reducing the organics (COD) and ammonia content of the effluent. It has been alsofound that the optimum alum dosage is around 200 mg/L (Fig. 2) which is recommended for obtaining agood quality effluent. With this dosage, removal efficiencies of 85 %, 55 % and 65 % can be achieved forSS, COD and P, respectively.

--._-~--

60

50 -

rl---... 40 -0>E~

n.. 30

oe1U) 20(f)

/

10

0./

0 100 200 300

Dose of Alum,400

mg/l500

-ss~lPLi1J

BCOD

1000

- 800

- 600

400

200

o

rl.........OJE

....oao

Figure 2. Effect of Alum Dosage on the Removal of Different Pollutants from Dairy FarmWastewater

Utilization of the effluent from the recommended alum treatment in irrigation of Lucerne grass isadvisable. It should not cause solids and organics buildup in the irrigated soil. However, there may be aconcern from increasing nitrogen loading of the soil due to continuous utilization of the effluent inirrigation. Another concern arises from the relatively high TDS and conductiVity (salt content) of theeffluent since alum treatment would contribute additional salts to the effluent and the settled sludge. Suchproblems could be overcome by frequent irrigation with fresh water according to well-calculated loading

Effluent quality for reuse in a dairy fann 85

rates of nitrogen and salts applied to soil. Moreover, selection of salt-tolerant plants is recommended.

Was~ewater reuse at the farm should also consider disinfection of the effluent by cWorination or otherpossIble means. This is deemed necessary to prevent any possible contamination by pathogens within theplant and/or the subsurface water in the vicinity. Proper management of waste at the farm should alsoinclude alternative arrangements during non-irrigating periods since the farm does not need daily irrigationand seasonal requirements may vary. Thus, satisfactory alternative arrangements must be made fordisposal during non-irrigating periods. In a properly engineered system, the surplus wastewater should bepossible to either store up or discharge elsewhere without causing any environmental hazards.

CONCLUSIONS

The following conclusions may be drawn based on the results of this study:• The dairy farm contributes considerable pollutant loads. Population equivalent based on BOD is 18,000

persons. The raw wastewater organics, solids and nutrient contents are high but daily variations inpollution loads are moderate.

• Plain sedimentation of raw wastewater can remove up to 53 % of the suspended solids but otherpollutants are removed at lower efficiencies. The characteristics of the primary-settled wastewater cannot satisfy the water quality criteria for irrigation reuse.

• Dilution of the primary-settled wastewater by mixing with the reject from reverse osmosis waterdemineralization unit improved its quality to a limited extent. Continuous reuse of the mixed effluent inirrigation of Lucerne grass over a period of one year resulted in a gradual deterioration of the harvest'squantity and quality.

• Chemical treatment using alum proved to be effective in reducing solids, organics and nutrients fromwastewater generated at the farm. An optimum dosage of 200 mg/L alum was observed. Thechemically-treated effluent meets the water quality criteria for reuse in irrigation but its salt content isrelatively high which may limit its application to agricultural lands.

ACKNOWLEDGMENT

The technical assistance received from the staff of the AI-Rawabi Dairy Farm, the EnvironmentalProtection and Safety Section of Dubai Municipalty and the Environmental Engineering Laboratory ofU.A.E University is gratefully appreciated. This research was supported by the Environmental ScienceM.Sc Program at U.A.E University for Mr. AI-Awadi., who is currently the industrial pollution controlofficer, Environmental Protection and Safety Health Department, Dubai Municipality, Dubai, U.A.E.

REFERENCES

APHA (1992). Standard Methods for the Examination of Water and Wastewater. 18th Ed., Am. Public

Health Association, Washington, D.C.Blan, F.e. and Navia, R. (1991). Treatment of Dairy Wastewater by. Chemical Coagulation. Proc. of 45th

Industrial Waste Conference. Purdue University, Lafayette, Indzana, pp. 681-689.Mann, EJ. (1990). Dairy Wastes Treatment and Dis~osal. Dairy Indus~ries International, 55, pp.8-19.Metcalf & Eddy, Inc. (1991). Wastewater Engineermg: Treatment, DIsposal, Reuse. 3rd Ed., McGraw-

Hill Book Co., New York, N.Y. . ' .'OdIum, C.A. et al. (1984). The economics of Waste Treatment m the DaIry Industry. InternatIOnal Dazry

Federation Bulletin, 184, pp. 72-79. . .R t Btl (1992). Chemical Pretreatment of Dairy Wastewater. 2nd Intern. Symposium on Waste

us en, . ea. P bl . A TO T-1dustrl'es Istanbul Turkey pp. 91-100. Schwer, C.B. and Clausen,Management ro ems In g -11 , " . 'J. C. (1989). Vegetative Filter Treatment of Dairy Milk House Wastewater. J. Environ Quallty, 18:

446-451.