Table of Contents

• Abstract
• Introduction
• Method
• Results and Discussion
• Conclusion
• Literature Cited

Agriculturalists in Israel and the United States are especially aware that the treatment of municipal wastewater is a costly process--one that frequently removes valuable nutrients from the water. By applying sewage treatment products such as sludge and effluents, the supply of irrigation water can be increased while reducing the need for chemical fertilizers. Thus, more fresh water can be diverted for domestic use.

Information dealing with sub-surface drip irrigation systems is limited. Therefore, the effect of hydraulic loading to the sub-surface soil system with municipal wastewater is the focus of this research study project. Of particular concern are the fate, transformation and transport of the constituents of wastewaters and sludges. Equally important are the retention and die-off of bacteria, and indicator organisms associated with sanitary wastewaters.

To determine the effectiveness of the drip-irrigation system two soil beds will be utilized, one consisting of the proposed sub-surface drip-irrigation system and one bed containing a four inch lateral septic line acting as the control. Wastewater collected from the Spicewood Wastewater Treatment Facility will be used to irrigate these beds at various loading rates, and samples will be collected for testing. Water clarity will be determined by monitoring the die-off of indicator organisms, including fecal coliform, and fecal streptococci. The removal of organic materials will be measured as Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD). Also monitored are theremoval and oxidation of nitrogenous species and the removal of phosphorous. These tests represent the normal parameters used when assessing the effectiveness of a municipal wastewater treatment plant.

Preliminary results demonstrate that the drip-irrigation system is a more effective method of wastewater treatment when compared to the lateral septic lines currently in use. The removal efficiencies for all parameters monitored are greater for the drip-system when loaded at a rate of approximately .5 gal/ft²/day, (20.37 L/m²/day, see Table 1). Also, the grass irrigated by the drip-system has less weeds and is much more lush and green than the control plot.

The data obtained from this project will help determine the usefulness of sanitary wastewaters for landscape and agricultural purposes in areas where water is scarce. The results will also provide information concerning the risk to human health due to possible contamination of groundwater resulting from the use of this drip-irrigation system utilizing municipal wastewaters and sludges on agricultural lands.

The use of secondary municipal effluent has become increasingly important as a source of irrigation waters in arid and semi-arid regions of the world. However, the question of contamination due to the constituents of these wastewaters has been a factor hindering its acceptance. Sub-surface drip-irrigation systems have been used for treatment of municipal wastewater in rural areas where large-scale treatment plants are not available. By utilizing the drip-irrigation system wastewater, can be used to irrigate landscape thus maximizing the recycling of this water.

The possibility of development outside the range of municipal sewage collection plants hinges on an economical method of wastewater treatment. Sub-surface drip-irrigation systems can enhance the transfer of pollutants to ground water because the soil horizon, which is the zone of maximum biofilter (chemical and biological) capacity, is bypassed. This region of the soil can also contain the greatest amount of pollutants. Therefore, the effectiveness of the sub- surface drip-irrigation system for the treatment and recycling of large volumes of sanitary wastewater needs testing.

The experimental plot utilizes a drip irrigation system consisting of a duplex centrifugal pump, disc filtration (3/4" Arkal Filter ®), a pulsing flow meter, pressure regulator fixed at 20 psi, and valves to control the hydraulic loading and dosing of the sub-surface drip-irrigation system. The Netafim Bioline ® pressure compensating dripperline was chosen for its superior emission uniformity. The sub-surface Bioline distributes the effluent at a low flow rate over the entire area, allowing slow lateral movement without percolation or surfacing. This dripperline also contains a patented antimicrobial filtration system that allows the dripper to cleanse itself and resist root intrusion, reducing the need for maintenance and increases reliability. In order to maintain the proper flow rate however, the drip-irrigation system is back-flushed and the disc filters are cleaned regularly. The dripper tubes will be placed six inches below the soil surface in the active root zone.

The control plot contains a four inch lateral septic line installed according to the Manual of Septic-Tank Practice. At the end of this septic line is a 90 degree elbow connected to a pipe which is run above the surface of the tank. A line attached to a submersible pump is used to supply influent to this pipe.

Both plots contain a stand of St. Augustine grass irrigated at a rate which will be gradually increased from approximately .5 to 1 gal/ft²/day (20.37 to 40.75 L/m²/day). The control pump emits influent at a rate of 300 gal/hr, (1135.62 L/hr) and the experimental pump emits influent at a rate of 5 gal/hr, (18.93 L/hr). Both pumps are controlled by electric timers. The control pump applies water three times daily and the experimental pump applies water six times daily, with time durations according to prescribed number of gal/ft²/day, (L/m²/day). The influent is drawn from two separate tanks which are filled twice weekly with wastewater. The effluent is collected from a tube which extends from the bottom of each tank.

Data from chemical analysis of influent and effluent will be recorded for each loading rate for at least two weeks beyond the stabilization of both systems. All water quality tests are conducted according to the procedures described in Standard Methods for the Examination of Water and Wastewater 16^th edition. These tests include BOD₅, COD, TKN, Total Phosphorus, and the membrane filter technique for Fecal Coliform and< Fecal Streptococci.

The entire project is located at the Center for Research in Water Resources on the J.J. Pickle Research Campus where state-of-the-art analytical equipment is available. Equipment for this project includes: incubators; microscopes; Inductively Coupled Argon Plasma and Atomic Absorption spectrophotometers for analysis of heavy metals; Gas Chromatograph/Mass Spectrometry system, High Pressure Liquid Chromatographs; Gas Chromatograph with Purge and Trap attachment for monitoring pesticides and other xenobiotic organic compounds; COD apparatus, TOC analyzers, pH meters, titration equipment , ovens, balances, ion probes, conductivity meters, etc. normally found in research facilities dealing with water and wastewater treatment and analyses. Also available are full time technicians at hand to assist project personnel and the basic infrastructure essential to conducting research.

Table 1: Influent and Effluent Quality Parameters and Removal Efficiencies for Both Experimental and Control Systems at a Loading Rate of .5gal/ft²/day, (20.37 L/m²/day).

System	Experimental	Control
Influent Quality Parameters
BOD5 (mg/L)	144.4	157.6
COD (mg/L)	204.0	281.6
Phosphorus (mg/L)	7.4	7.0
TKN (mg/L)	54.9	52.8
E. Coli (Colonies/100ml)	413709.1	386250.0
Fecal Strep (Colonies/100ml)	148969.7	175666.7
Effluent Quality Parameters
BOD5 (mg/L)	0.9	8.8
COD (mg/L)	13.3	29.7
Phosphorus (mg/L)	0.2	1.6
TKN (mg/L)	0.9	6.1
E. Coli (Colonies/100ml)	9.1	24475.0
Fecal Strep (Colonies/100ml)	2.1	21600.6
Organic Removal Efficiencies
BOD5 (percent)	99.389	94.393
COD (percent)	93.499	89.459
Die-Off of Indicator Organisms
E. Coli (percent)	99.998	93.663
Fecal Strep (percent)	99.999	87.704
Removal and Oxidation of
Nitrogen (percent)	98.433	88.506
Removal of Phosphorus
(percent)	96.914	77.125

These results demonstrate that the drip-irrigation system is more effective at removing contaminants than the lateral septic line at a rate of .5 gal/ft²/day, (20.37 L/m²/day). Fecal Coliform data was erroneous for this rate due to an error in the incubation time of the samples, therefore their results have been excluded from the above table.

From visual inspection of both plots, the experimental plot had a more dense and greener stand of grass with relatively no weeds. The control plot contained large yellow patches of dry grass and was overrun with weeds. The weeds in the control plot benefited from the irrigation pipe being much deeper than the root zone of the grass, allowing the weeds long root system to dominate the water supply. In the experimental tank the grass was so thick that there was little room for competition, leaving the plot virtually weed free.

More study is needed however, in order to monitor the system at different loading rates. Furthermore, study must be continued through the months when the grass is dormant in order to determine this effect on nutrient uptake and the corresponding quality of the effluent.

A drip-irrigation system is effective because it uses low-doses of wastewater. By watering slowly but regularly, the pollutants have time to accumulate in the root structures of the plants. Another benefit to this system is that water is focused on the root zone, maximizing plant development while reducing weed growth.

The results of this project thus far demonstrate that the Bioline® sub-surface drip-irrigation system is more effective at treating municipal wastewater than the traditional four inch lateral septic line. These results will help determine the usefulness of the sub-surface drip-irrigation system in renewing large volumes of wastewater. With this data, it will be possible to better understand the feasibility of industrial, agricultural, and residential development in water-short areas and regions lacking the collection facilities of a wastewater treatment plant.

American Public Health Association (APHA), 1992. Standard Methods for the Examination of Water and Wastewater (18^th Edition). Washington D.C.

The Daily Texan 7 August 1995, sec. A: 1

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