Progress 10/01/04 to 09/30/09
Outputs
OUTPUTS: The fate of pollutants from subsurface drip irrigation of septic tank effluent has been studied over the past five years. Field experiments using containers packed with loamy sand, sandy loam, and silt loam soils were developed and tested at the UC Davis wastewater treatment facility. Data were analyzed in the Hydrus 2D Model, which predicts adsorption and biodegradation of pollutants in soils. Nitrogen removal rates in the field tests ranged from 63% to 95%, despite relatively low levels of carbon. Modeling indicated that the greatest nitrogen losses (30% to 70%) were predicted for medium to fine textured soils. Restrictive layers or capillary breaks appeared necessary in coarse soils to achieve substantial nitrogen losses. The field data indicated that slow nitrogen transport enhances nitrogen losses and plant uptake opportunity. Modeling studies continued this past year using long-term simulations of nitrification and denitrification as a function of air-filled porosity. For maximum denitrification, it appears that the liquid for subsurface drip dispersal should be well filtered, partially oxidized effluent. Based on the container test results, leaving some carbon in effluent and nitrogen in the ammonia form is beneficial for denitrification. It also appears that the application rate should be high enough to keep the soil relatively moist but not fully anaerobic nor with excessive preferential flow. The ideal soil moisture appears to be a compromise, depending upon what constituents are most important to remove. While the Hydros 2-D results provide reasonable correlation with the field data, a model that better represents the actual biochemical processes would likely provide further insights, especially for transient conditions. A five-year project was also completed this past year comparing disc and screen filters for removing algae (Spirogyra) from surface irrigation water used in microirrigation. Plastic disc and screen filters of four mesh sizes were evaluated for different algae concentrations. Laboratory experiments determined the rates of algae buildup on different size disc and screen filters with waters of different suspended solids concentrations. Clogging in a disc filter was shown to proceed in a linear fashion; whereas, for a screen filter clogging proceeded very slowly at first, but rapidly increased once a level of contaminant formed on the screen surface. A field study using Netafin Techline laterals was conducted using pond irrigation water. Water was pumped to two subunits, one with a screen filter and the other with an equivalent disc filter. The Statistical Uniformity Coefficients, calculated from emitter discharge data, were high for all original laterals, and following 500 hours of operation they decreased marginally for the disc filter subunit laterals and decreased significantly for the screen filter subunit laterals. This observation indicates that more impurities were passing through screen filters than disc filters, supporting the laboratory data. Results from this project have been presented in national symposiums and technical journals. Further dissemination of these studies is planned. PARTICIPANTS: Students and visiting scholars: Shalamu Abudu, Visiting scholar (China), Biological and Agricultural Engineering, UC Davis Robert Beggs, doctoral student, Biological and Agricultural Engineering, UC Davis Jerry Wang, undergraduate student, Biological and Agricultural Engineering, UC Davis Dennis Cararo, Visiting scholar (Brazil), Biological and Agricultural Engineering, UC Davis Harold Leverenz. Post-doctoral Researcher, Civil and Environmental Engineering, UC Davis Professional Colleagues: Jan Hopmans. Professor, Land, Air and Water Resources, UC Davis Freddie R Lamm. Professor, Northwest Research-Extension Center, Kansas State University George Tchobanoglous. Professor Emeritus, Civil and Environmental Engineering, UC Davis Todd Trooien. Professor, Agricultural and Biosystems Engineering, South Dakota State University Muluneh Yitayew. Professor, Agricultural and Biosystems Engineering, University of Arizona TARGET AUDIENCES: Primarily microirrigation researchers and manufacturers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Subsurface drip systems hold promise for the application of non-disinfected effluent from small wastewater systems at shallower depths, over larger areas, and at lower rates than has been possible with other effluent dispersal methods. This study has shown that nitrogen removal and utilization are especially effective in medium to fine soils and for soils with shallow restrictive or capillary break layers. For sandy soils, the nitrogen loading rate is more limiting than the hydraulic loading rate. While nitrogen considerations may indicate that subsurface drip dispersal is not practical on well drained sandy soils, it is still far more suitable for sandy soils than is conventional leach field dispersal. Conventional leach field dispersal depends almost entirely on dilution for reducing nitrogen concentrations, with minimal opportunity for plant uptake or denitrification, while subsurface drip dispersal needs much less dilution. The minimum area required for a drip system to maintain an acceptable groundwater nitrate-N concentration can be estimated using a mass balance approach developed in this project. One of the ancillary benefits of drip dispersal is that water and nutrients can be more effectively supplied to landscape plants, thereby conserving fresh water and reusing nutrients. In California there are over two million acres in agriculture using microirrigation systems. The major problem facing this technology is clogging or partial clogging of the emitters. Clogging creates non-uniformity in water application that lowers water use efficiency. The primary source of irrigation water in the state is from lakes and rivers, which is not ideal for microirrigation since surface water contains aquatic plants that easily plug emitters. This project has shown that disc filtration is relatively effective in removing these organic impurities. Of the various mesh sizes studied, the ones with larger openings, 180 and 200 microns, were inefficient in removing high percentages of algal contaminant. The filters with smaller opening sizes, 100 and 130 microns, were found suitable for algae removal and for a variety of emitters. Laboratory data indicated that the disc filters removed algae at a rate linear to the total water flow, whereas the algae removal rate was relatively low initially for screen filters, but accelerated once the pressure drop across the screen reached 0.3 bar. Disc filters were shown to remove greater quantities of algae and clean more water than screen filters for any specified pressure drop. For example, for a pressure drop of 1.2 bars, 130-micron disc filters might remove twice the algae and clarify four times more water than 130-micron screen filters. Field studies corroborated the laboratory findings. In the field, screen filters were not as efficient as disc filters for removal of Spirogyra algae, resulting in a higher percentage of the screen filter emitters becoming partially plugged following 500 hours of operation. Laboratory data with algal laden water showed that disc filters were cleaned with less back-flush water than required for equivalent screen filters.
Publications
- Trooien, T.P., Hills, D.J., and Lamm, F.R. 2009. Using SDI to effectively irrigate with biological effluent. Proceedings of the 2009 Irrigation Association Technical Conference, San Antonio, TX.
- Beggs, R., Hills, D., Tchobanoglous, G., and Hopmans, J. 2010. Fate of nitrogen for subsurface drip irrigation of effluent from small wastewater systems. Water Research (Pending).
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Laboratory studies continued this past year evaluating disc and screen filters for removing algae (Spirogyra) from surface irrigation water. Amiad plastic filters of the following sizes were evaluated for different algae concentrations: Disc (100, 130, 180 micron openings) and Screen (100, 130, 200 micron openings). Preliminary results are as follows. The larger opening sizes, 180 and 200 microns, were found to be inefficient in removing high percentages of algae contaminant and should not be considered for microirrigation using surface waters. The smaller opening sizes, 100 and 130 microns, appear suitable for a variety of emitters, and the disc filters appear superior to screen filters for algae removal. The disc filter removes algae at a rate linear to the total water flow through it, whereas the algae removal rate is relatively low initially for screen filters, but accelerates once the pressure drop across the screen reaches 0.3 bar. Disc filters remove greater quantities of algae and clean more water than screen filters for any specified pressure drop. For a pressure drop of 1.2 bars, 130-micron disc filters remove twice the algae and clarify four times more water than 130-micron screen filters. A special cleaning device, using jets of water, was fabricated for evaluating algae removal efficiency from the clogged filters. Results indicate that higher rpm and slower lateral movement of the water jets improved the cleaning process for either filter type. Disc filters however were cleaned with less water than needed for the equivalent opening-size screen filters. PARTICIPANTS: David J. Hills, Professor Emeritus, Biological and Agricultural Engineering UC Davis TARGET AUDIENCES: Primarily microirrigation researchers and manufacturers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
There are about two million acres in California currently using microirrigation systems, which represents 25 percent of the total irrigated area in the state. The major problem facing this technology is clogging or partial clogging of the emitters. Clogging creates non-uniformity in water application that lowers water use efficiency. The primary source of irrigation water in the state is from lakes and rivers, which are not ideal for microirrigation since surface water contains aquatic plants, such as algae, that easily plug microirrigation emitters and is difficult to remove from the water without the use of elaborate sand filtration equipment. In this study, simple, less expensive disc and screen filters are being evaluated for their algal removal effectiveness under a variety of conditions.
Publications
- No publications reported this period
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Progress 01/01/07 to 12/31/07
Outputs
Both projects that were reported in the 2006 report continued into 2007. A field study was conducted which compared disc and screen filtration of algae (Spirogyra) from pond irrigation water. Water was pumped to two subunits, one using a 155 mesh screen filter and the other using a 155 mesh disc filter. Each subunit had three 25 m Netafin Techline laterals (pressure compensating emitters: 2.3 l/h with 300 mm spacing). Every 24 hrs the filters were washed clean and the residue collected for further analysis. Following 100 hrs of operation and again after 500 hrs the Statistical Uniformity Coefficient, as defined by ASAE Standard EP458, for each lateral was calculated, based on the discharges from 20 randomly selected emitters. The average uniformity coefficient was very high for the original laterals and decreased gradually for the disc filter subunit and more significantly for the screen filter subunit. This project is continuing in the laboratory, evaluating algal
removal efficiency based on filtration surface area and opening size. The field and modelling study pertaining to the fate of pollutants from subsurface drip irrigation of septic tank effluent concluded in 2007. Major conclusions from field data and the modeling study on the effectiveness of effluent nitrogen removal and utilization are: (1) Nitrogen removal is especially effective in medium to fine soils and soils with shallow restrictive or capillary break layers. In these soils, a 50% nitrogen loss is not unreasonable to expect. The long retention time in the soil column provides a good opportunity for denitrification, even with less than ideal reaction rate conditions. (2) Higher application rates increase the rate of denitrification, but this effect is partially offset by the shorter residence time in the soil column. Longer application durations are beneficial to both denitrification and distribution uniformity, but there are practical limits to the duration of effluent
applications. Keeping the soil moist, with intermittent durations or layers of near-saturation conditions will provide the best overall nitrogen removal conditions.
Impacts
There are about two million acres in California currently using microirrigation systems, which represents 25 percent of the total irrigated area in the state. The major problem facing this technology is clogging or partial clogging of the emitters. Clogging creates non-uniformity in water application, that lowers water use efficiency. The primary source of irrigation water in the state is from lakes and river, which is not ideal for microirrigation since surface water contains aquatic plants, such as algae, that easily plug microirrigation emitters and is difficult to remove from the water without the use of elaborate sand filtration equipment. Simple, less expensive disc filters are being evaluated for their algal removal effectiveness under a variety of conditions. (b). Subsurface drip systems hold promise for the application of non-disinfected effluent from small wastewater systems at shallower depths, over larger areas, and at lower rates than has been possible
with other effluent dispersal methods. One of the ancillary benefits of subsurface drip irrigation is that water and nutrients can be more effectively supplied to landscape plants, thereby conserving fresh water and reusing nutrients.
Publications
- Beggs, R.,Tchobanoglous, D., Hills D.,and Hopmans, J. 2008. Subsurface Drip Irrigation Dispersal For Small Wastewater Systems. ASCE Journal of Environmental Engineering. In Press.
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Progress 01/01/06 to 12/31/06
Outputs
A project initiated in 2005 for comparing disc and screen filtration of algae from surface irrigation water continued into 2006 with both laboratory and field studies. The laboratory phase considered the effects of rotational and longitudinal movements of filters within a cleaning chamber under different water jet scenarios for removing Spirogyra algae from partially clogged screen surfaces. Results indicate that disk filters were cleaned with less water and energy than the equivalent opening-size screen filters. This investigation was later extended to the field, using surface water with natural occurring algae contaminates. While the field study is continuing, the initial results are similar to those of the laboratory work with definable algal enriched water. Clogging in a disc filter proceeded in a linear fashion, whereas, for a screen filter, clogging proceeded very slowly at first, but rapidly increased once a level of contaminant formed on the screen surface.
After all data are furthered analyzed, the field study may be modified appropriately and continued into 2007. A project pertaining to the fate of pollutants from subsurface drip irrigation of septic tank effluent also continued during 2006. Based on calibrated Hydrus 2D modeling results, it was found that a system designed for efficient irrigation generally minimized annual nitrate percolation. The model predicted the greatest nitrogen losses (30 to 70%) for medium to fine texture soils. Restrictive layers or capillary breaks were necessary in coarse soils to achieve substantial nitrogen losses. The slow nitrogen transport with subsurface drip enhanced nitrogen losses and plant uptake opportunity. Other design and operational issues evaluated included water distribution uniformity and plugging. Distribution uniformity was found to be sensitive to elevation differences in the distribution system because of system drainage after completion of each irrigation. Surfacing of effluent was
an issue in fine soils in the container tests, indicating the importance of soil macropores for temporarily holding applied effluent. Gradual emitter plugging was observed, but flushing and other practices kept emitter flow rates in a reasonable range. Based on this research and other field experience, subsurface drip irrigation can be an environmentally sound method for reuse of effluent from small wastewater systems.
Impacts
(a) There are about two million acres in California currently using microirrigation systems, which represents 25 percent of the total irrigated area in the state. The major problem facing this technology is clogging or partial clogging of the emitters. Clogging creates non-uniformity in water application, that lowers water use efficiency. The primary source of irrigation water in the state is from lakes and rivers, which is not ideal for microirrigation since surface water contains aquatic plants, such as algae, that easily plug microirrigation emitters and is difficult to remove from the water without the use of elaborate sand filtration equipment. Simple, less expensive disc filters are being evaluated for their algal removal effectiveness under a variety of conditions. (b) Subsurface drip systems hold promise for the application of non-disinfected effluent from small wastewater systems at shallower depths, over larger areas, and at lower rates than has been
possible with other effluent dispersal methods. One of the ancillary benefits of subsurface drip irrigation is that water and nutrients can be more effectively supplied to landscape plants, thereby conserving fresh water and reusing nutrients.
Publications
- Cararo, D. C., Botrel, T. A., Hills, D. J. and Leverenz, H. L. 2006. Analysis of clogging in drip emitters during wastewater irrigation. Applied Engineering in Agriculture 22(2):251-257.
- Trooien, T. P. and Hills, D. J. 2007. Chapter 9. Application of biological effluent. In Microirrigation for Crop Production, Lamm, F. R., Ayars, J. E. and Nakayama, F. S., editors. Elsevier Press pp. 329-356.
- Hills, D. J. and Yitayew, M. 2007. Chapter 14. Bubbler irrigation. In Microirrigation for Crop Production, Lamm, F. R., Ayars, J. E. and Nakayama, F. S., editors. Elsevier Press pp. 553-573.
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Progress 01/01/05 to 12/31/05
Outputs
This past year a project was initiated that compared disc and screen filters for removing algae from surface irrigation water. Its goal is to objectively evaluate disc filtration for removal of algae (Spirogyra) and to compare its performance with that of screen filters, For preliminary tests, three mesh sizes (80,120,155) were evaluated in the laboratory with different algal loading rates. Initial observations indicate that the clogging characteristics of disc and screen filters are different. Clogging in a disc filter proceeds in a linear fashion, whereas, for a screen filter, clogging proceeds very slowly at first, but rapidly increases once a level of contaminant forms on the screen surface. Overall, the disc filter is more efficient in filtering the algal contaminated water. The time and suspended solids retained on a disc filter for a predetermined pressure drop are both more than twice that of a screen filter. Removal of the impurities of the disc filter is
also more efficient than it is on a comparable screen filter. Laboratory research is continuing, before initiating a field study in 2006. The project pertaining to the fate of pollutants from subsurface drip irrigation of septic tank effluent has continued this past year. Following the initial modeling report for last year, container tests with packed loamy sand, sandy loam, and silt loam soils were developed and tested at the UC Davis wastewater treatment facility. Nitrogen removal rates in these tests ranged from 63% to 95%, despite relatively low levels of carbon. Advanced modeling tests indicated that the greatest nitrogen losses (30% to 70%) were predicted for medium to fine textured soils. Restrictive layers or capillary breaks were necessary in coarse soils to achieve substantial nitorgen losses. The slow nitrogen transport with subsurface drip enhanced nitrogen losses and plant uptake opportunity.
Impacts
There are 1.7 million acres in California currently using microirrigation systems, which represents 20 percent of the irrigated area in the state. The major problem facing this technology is clogging or partial clogging of the emitters. Clogging creates non-uniformity in water application, that lowers water use efficiency. The primary source of irrigation water in the state is from lakes and river, which is not ideal for microirrigation since it contains aquatic plants, such as algae that easily plug microirrigation emitters, and is difficult to remove from the water without the use of elaborate sand filtration equipment. Simple, less expensive disc filters are being evaluated for their algal removal effectiveness under a variety of conditions. Design criteria and management procedures are being developed.
Publications
- Beggs, R. A. 2005. Nutrient removal in subsurface drip application of onsite wastewater system effluent. Ph.D. Dissertation. University of California, Davis. 155 pp.
- Cararo, D. C., Botrel, T. A., Hills, D. J. and Leverenz, H. L. 2006. Characterization of drip emitter clogging in wastewater irrigation. Applied Engineering in Agriculture (In Press).
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