Progress 09/17/01 to 09/16/06
Surface water quality in 25 % of rivers in Texas is limited by pollution. Bacterial contamination is the limiting factor in 60 % of the polluted rivers. Pollution of these rivers must be reduced by better control of non-point sources which include both agriculture and urban sectors. The sources and quantities of the pollutants must be identified and practices put into place to control the pollution. The purpose of this project is to better understand how non-point source pollution influences water quality and how it may be reduced. A primary cost of subsurface flow constructed wetlands is the fill medium. Using chipped tires as an alternative to gravel reduces the cost of construction by approximately 30 percent which makes the use of this technology for on-site wastewater treatment more attractive. The major accomplishment from our work with bacterial indicators in manure is the demonstration that E. coli and fecal streptococci survive well in aged manure samples from
cattle, horse, and sheep.
Our results help explain why streams may continue to be polluted by fecal bacteria long after the livestock have been removed. It also raises concerns about only sampling fresh manure for isolation of bacteria used in bacterial source tracking since the reservoir of indicator bacteria would be much greater in aged manure since it is more plentiful. It is likely that including isolates in a known source library from aged manure may increase the capability of bacterial source tracking in identification of the animal types polluting streams.
- No publications reported this period
Progress 01/04/04 to 12/04/04
Subsurface flow constructed wetlands (SFCWs) are an increasingly common method for on-site treatment of wastewater. Gravel is the most common type of wetland fill medium, but the overabundance of scrap tires has initiated alternate uses. Chipped rubber tires are less dense and less expensive than gravel medium. This study determined the treatment efficiency of SFCWs filled with gravel or tire chip media to reduce P content in domestic wastewater, both in field practices and in experimental columns. The P content in the influent and effluent of six SFCWs filled with tire chip medium and six SFCWs filled with gravel were monitored for 5 to 16 months. Additionally, five columns filled with tire chips and five filled with gravel were evaluated for 3 months for their ability to reduce P. There was a clear difference between medium types in reduction of P. Soluble P in the effluent averaged 1.6 mg per liter in the tire chip-filled wetlands and 4.8 mg per liter in the
gravel-filled wetlands. Phosphorus reduction was 60 percent in columns filled with tire chips and only 17 percent in columns filled with gravel. Greater P reduction most likely occurred in the tire chip-filled wetlands and columns because the Fe from exposed wires in shredded steel-belted tires complexed with P to create an insoluble P compound. Tire chips may be a better fill medium for SFCWs than gravel because of higher porosity, lower cost, and greater reduction of P in effluent. Fecal coliforms and fecal streptococci are the primary bacterial indicators of water pollution and livestock are known contributors to stream pollution. Data on the populations of fecal coliforms and fecal streptococci in aged manure naturally deposited by livestock in the field were measured. These data will be useful for activities related to bacterial source tracking and determining maximum daily bacterial loading of streams. We measured populations of fecal streptococci and E. coli in fresh and aged
cattle, horse and sheep manure. Populations of indicator bacteria in aged manure were often as high as in fresh manure from horse and sheep. There was a 100 fold drop in the population of fecal coliform numbers in aged cattle manure in pastures but not for cattle in pens. Libraries of isolates used in bacterial source tracking should include isolates from both fresh and aged manure to better represent the bacterial source loading of streams.
A primary cost of subsurface flow constructed wetlands is the fill medium. Using chipped tires as an alternative to gravel reduces the cost of construction by approximately 30 percent which makes the use of this technology for on-site wastewater treatment more attractive. The major accomplishment from our work with bacterial indicators in manure is the demonstration that E. coli and fecal streptococci survive well in aged manure samples from cattle, horse, and sheep. Our results help explain why streams may continue to be polluted by fecal bacteria long after the livestock have been removed. It also raises concerns about only sampling fresh manure for isolation of bacteria used in bacterial source tracking since the reservoir of indicator bacteria would be much greater in aged manure since it is more plentiful. It is likely that including isolates in a known source library from aged manure may increase the capability of bacterial source tracking in identification of
the animal types polluting streams.
- Richter, A.Y. and R. W. Weaver. 2003. Treatment of domestic wastewater by subsurface flow constructed wetlands filled with gravel and tire chip media. Environ. Tech. 24: 1561-1576.
- Wright, A. L. and R. W. Weaver. 2004. Fertilization and bioaugmentation for oil biodegradation in salt marsh mesocosms. Water, Air, and Soil Pollution 156: 229-240..
- McGilloway, R.L. and R. W. Weaver. 2004. Effects of drying on nitrification activity in zeoponic medium used for long-term space missions. Habitation 10: 15-19.
- Meunchang, Sompong, S. Panichsakpatana, and R.W. Weaver. 2004. Co-composting of filter cake and bagasse; by-products from a sugar mill. Bioresource Technology (in press).
- Meunchang, Sompong, S. Panichsakpatana, and R.W. Weaver. 2004. Inoculation of sugar mill by-products compost with N2-fixing bacteria. Plant Soil (In press).
Progress 01/01/03 to 12/31/03
Brilliant blue dye and bromide were used to follow water flow through a constructed sub-surface flow constructed wetland. The tracers showed that water flowed uniformly across the width of the wetland but there was not uniform mixing with depth over 40cm. Water was dispersed as it flowed through the wetland which may aid in aeration. Root masses caused preferential flow of water around the masses. Wastewater depth of 20 cm provided more reduction in BOD than a wastewater depth of 40 cm even though the increased depth doubled the detention time. The surface area exposed air was more important than depth. Ultraviolet light was effective in disinfecting wastewater from wetlands but maintenance was problematic. The bulbs had to be cleaned on a monthly basis to remove biofilms to maintain effective operation.
Design criteria of constructed subsurface flow wetlands for on-site domestic wastewater treatment should consider the incorporation of plants and foot print size. Relatively shallow wetlands of 20 cm water depth were as effective as 40 cm deep wetlands. The deeper depth doubled the cost of gravel which is the main materials cost but did not improve treatment. Ultraviolet light disinfection of effluent killed pathogens but frequency of maintaining the units on constructed wetlands made them impractical. Liquid chlorination systems seem more practical for long term usuage.
- Weaver, R.W., M. C. Stecher, and K.J. McInnes. 2003. Water flow patterns in subsurface flow constructed wetlands designed for on-site domestic wastewater treatment. Environ. Tech. 24: 77-86.
- Stecher, M. C. and R. W. Weaver. 2003. Effects of umbrella palms and wastewater depth on wastewater treatment in a subsurface flow constructed wetland. Environmental Technology 24: 471-478.
- McGilloway, R. L., R.W. Weaver D.W. Ming, and J.E. Gruener. 2003. Nitrification in a zeoponic substrate. Plant Soil 240: 127-132.
- Richter, A.Y. and R. W. Weaver. 2003. Ultraviolet disinfection of effluent from subsurface flow constructed wetlands. Environ. Tech. 24: 1175-1182.
Progress 01/01/02 to 12/31/02
Wastewater effluent from constructed subsurface flow wetlands is recyled onto the landscape or placed into the soil near the site of treatment.Quality of the effluent is important as related to public health and determining the operating life of disposal areas. Our research indicated adding plants to these wetlands only contributed to about 10% of the treatment and were not necessary for achieving good treatment. Wetland depth exceeding 20 cm did not enhance treatment even though detention time was increased by maintianing the same hydraulic loading. Adding wastewater into soil through drip tubing buried at 15 cm resulted in frequent occurances of water reaching the soil surface. Bacteria were not removed from the wastewater before it reached the soil surface. Buring the drip tubing 12 inches deep reduced occasions when wastewater surfaced. The soil type had a large influence on surfacing of wastewater in poorly drained soils.
Maintenance of subsurface flow wetlands may be reduced by not growing plants without significant reduction in treatment of the wastewater. Capital costs will be saved by reducing the qauntity of gravel needed since shallow wetlands functioned as well as deeper wetlands. Applying drip tubing into the soil to a depth of 30 cm reduces public health threats from wastewater surfacing.
- Franti,J.M.,Weaver,R.W.,and McInnes, K.J.2002. Surfacing of domestic wastewater applied to soil through drip tubing and reduction in numbers of Escherichia coli. Environ.Tech.23:1027-1032.
- Stecher,M.C. 2001. Wastewater treatment and flow patterns in an onsite subsurface flow constructed wetland. Master of Science Thesis, Texas A&M University, College Station, Tx.
- Franti, J.M. 2001. Movement and treatment of water containing Escherichia coli applied to soil by subsurface drip emitters. Master of Science Thesis, Texas A&M University, College Station, Tx.
Progress 01/01/01 to 12/31/01
Secondary treatment of wastewater from homes without central sewage treatment facilities is becoming more popular. Subsurface flow constructed wetlands provides on-site treatment of domestic wastewater and helps protect the environment from contamination with human pathogens. Disinfection of the effluent was achieved by use of chlorination or ultraviolet light. Utraviolet light proved to be an effective method without the high maintenance requirements of tablet chlorination. Twenty subsurface flow wetlands have been constructed and are being monitored for efficacy in treatment of domestic wastewater. The wetlands are providing secondary quality effluent with respect to biological oxygen demand but are not consistent with respect to total suspended solids. Fine particles in the gravel or rubber tire media contribute total suspended solids that are released following rain and appear in the effluent.
Subsurface flow constructed wetlands will be accepted as an alternative technology for on-site treatment of domestic wastewater. The result will be reduced environmental contamination of soil and surface water with nutrients and pathogens.
- Weaver, R.W., Lane, J.J. Johns, M.J. and Lesikar, B.J. 2001. Uptake of 15N by macrophytes in subsurface-flow wertlands treating domestic wastewater. Environ. Tech. 22: 837-843.
Progress 01/01/00 to 12/31/00
There is a growing interest in using constructed subsurface flow wetlands to treat domestic wastewater before application to land. Design of the wetlands has not been adequately tested to optimize sizing and inclusion of plants. Wasterwater treatment was not improved by having a wetland deeper than 30 cm eventhough detention time was increased. Planted cells reduced BOD and ammonium values below those of unplanted cells. High pressure drip tubing was an effective method for applying treated wastewater to soil. A critical factor was depth of placing the drip tubing. Tubing installed at greater than 30 cm did not have water reaching the soil surface but installation at 15 cm frequently resulted in wastewater surfacing. Populations of fecal coliforms in surfaced water was not reduced by having passed through soil. Probably, because by-pass flow paths were operational and there was little contact with the soil matrix.
Constructed subsurface flow wetlands are being installed for demonstration purposes to reduce public health hazards from untreated wastewater reaching surface waters. Application of the wastewater through high pressure drip tubing into the soil further reduced the liklihood of polluted water mixing with surface waters.
- Neralla,S.and Weaver,R.W. 2000. Phytoremediation of domestic wastewater for reducing populations of Escherichia coli and MS-2 coliphage. Envrion. Tech. 21:691-698.
- Neralla,S. and Weaver,R.W. 2000. Improvement of domestic wastewater quality by subsurface flow constucted wetlands. Bioresource Tech. 75: 19-25.
Progress 01/01/99 to 12/31/99
Subsurface flow constructed wetlands are gaining importance for on-site treatment of domestic wastewater. Use of plants in such wetlands is common but needed evaluation for role in phytoremediation. Phytoremediation reduced populations of Escherichia coli and MS-2 coliphage, biological oxygen demand, concentrations of ammonium and phosphorus. Eight constructed wetlands in Texas were evaluated for their effectiveness in treating domestic wastewater. The biological oxygen demand of the water was reduced 80 to 90%. Populations of fecal coliforms were reduced 90 to 99% without chlorination. With chlorination the populations were completely eliminated. The wetlands were not effective in reducing concentrations of phophorus but reduced nitrogen concentrations by approximately 40%.
Subsurface flow constructed wetlands provide an effective and economical way of treating domestic wastewater before application to land. Treatment reduces the potential for ground and surface water contamination with pathogens and nitrogen. It also provides odor control.
- Neralla,S.,Weaver, R.W., Varvel, T.W. and Lesikar,B.J. 1999. Phytoremediation and on-site treatment of septic effluents in sub-surface flow constructed wetlands. Environ. Tech. 20:1139-1146.
- Munoz,A.E.and Weaver, R.W. 1999. Competition between subterranean clover and ryegrass for uptake of 15N-labeled fertilizer. Plant Soil 211:173-178.
- Trotman,A.P. and Weaver, R.W. 1999. Survival of rhizobia on arrowleaf clover seeds under stresses of seed-coat toxins, heat and desiccation. Plant Soil (in press).
Progress 01/01/98 to 12/31/98
Water from an estuary was supplemented with NH4+ and P to determine concentrations of N and P adequate for supporting exponential growth of bacteria utilizing crude oil, and to determine maximum rates of N and P uptake. Oil-degrading microorganisms were obtained by enrichment culture of indigenous oil-utilizing microorganisms in water. Ammonium at a concentration of 5.5 mM was limiting to growth of bacteria on crude oil. Exponential growth occurred at concentrations higher than 30 mM NH4+. P concentration of 0.13 mM was limiting to growth of bacteria on crude oil. Exponential growth occurred at 1.8 mM P. Maximum NH4+ consumption rate was 426 mg NH4+ L-1 hr-1 and maximum uptake rate of P was 48 mg P L-1 hr-1. Uptake of N and P with time showed zero-order kinetics, likely due to substrate solubility limitations. The uptake ratio of N:P was approximately 7:1 on a weight basis. Natural concentration of N and P in marine and estuarine systems after hydrocarbon spillage may
not initially limit oil biodegradation but may become limiting if adequate flux does not occur to replenish N and P depleted during microbial consumption.
- Chang, Z.Z. and R.W. Weaver. 1998. Organic bulking agents for bioremediation in soil. Bioremediation J. 1:173-180.
- Rhykerk, R.H., D. Sen, K.J. McInnes and R.W. Weaver. 1998. Volatilization of crude oil from soil amended with bulking agents. Soil Science 163:87-92.
- Rhykerd, R.H., C. Crews, K.J. McInnes and R.W. Weaver. 1999. Impact of bulking agents, forced aeration, and tillage on remediation of oil-contaminated soil. Bioresource Technology 67:279-285.
- Strynar, M., D. Sen, and R.W. Weaver. 1999. Nitrogen and phosphorus for growth of oil-degrading microorganisms in sea water. Bioremediation J. 2: (In Press).
Progress 01/01/97 to 12/31/97
Addition of bulking agents to soil contaminated with crude oil may enhance the rate of bioremediation and decrease losses of hydrocarbons due to volatilization. Materials having potential to enhance bioremediation and reduce volatilization were tested in the laboratory. Soil itself reduced volatilization by 17% compared to volatilization from a free oil surface and addition of grass hay, sawdust, peat, or charcoal reduced volatilization by a further 10%. Adding bulking agents may not be a practicable solution for effectively reducing volatilization losses of hydrocarbons because most losses occur during the first few hours after a spill and before the agents could be applied. The bulking agents were very useful in enhancing the rate of biodegradation. Addition of organic bulking agents to soil contaminated with oil increased populations by approximately ten times 40 and 80 d after addition of bulking agents but did not significantly increase the numbers of hydrocarbon
degrading microorganisms above that of the nonbulked control. Bulking agents increased the quantity of total petroleum hydrocarbons degraded by approximately 20% during the first 40 d after being added. It appears the addition of bulking agents may enhance the rate of decomposition of total petroleum hydrocarbons by stimulation of the general heterotrophic population of microorganisms but the influence may not be sustained to influence the extent of decomposition when several months are involved.
- Chang, Z.Z. and R.W. Weaver. 1997. Nitrification and utilization of ammonium and nitrate during oil bioremediation at different water potentials. J. Soil Contamination 6(2):149-160.
- Neralla, S. and R.W. Weaver. 1997. Inoculants and biodegradation of crude oil floating on marsh sediments. Bioremediation J. 1:89-96.
- Chang, Z.Z. and R.W. Weaver. 1998. Organic bulking agents for bioremediation in soil . Bioremediation J. (in press).
- Rhykerd, R.H., D. Sen, K.J. McInnes and R.W. Weaver. 1998. Volatilization of crude oil from soil amended with bulking agents. Soil Science (in press).
Progress 01/01/96 to 12/30/96
Reclaiming oil contaminated water and soil by bioremediation depends on having adequate nutrient concentrations for microbial activity. Addition of excessiveamounts of nutrients may not be advisable because of potential pollution from nitrates andeutrophication. Formation of nitrates may not be a problem if ammonium is used as the nutrient source fornitrogen because crude oil is toxic to nitrifying bacteria and inhibited conversion to nitrate incontaminated soil. Nutrients added to salt marsh mesocosms growing #Spartina alterniflora# to enhance oilbiodegradation were taken up by the plants and adsorbed by soil. Nitrogen remained higher than background levels for at least 2 weeks following fertilization but increased levels ofphosphorus were present for at least four weeks after fertilization. Frequent application of nitrogenfertilizer would be needed to maintain concentrations needed for oil bioremediation in the water columnand to replenish nutrients lost during
tidal exchange of water. It does not appear thatinoculants are needed to enhance bioremediation of crude oil in salt marsh systems when adequatenutrients are provided.
- CHANG, Z.Z. and R.W. WEAVER. 1997. Nitrification and utilization of ammonium andnitrate during oil bioremediation at different water potentials. J. Soil Contamination ( In press).
- NERALLA, S. and R.W. WEAVER. 1997. Inoculants and biodegradation of crude oil floating on marsh sediments. Bioremediation J. (In press).
- WRIGHT, A.L. , R.W. WEAVER, and J.W. WEBB. 1996. Concentrations of N and P in floodwater and uptake of 15N by Spartina alterniflora in oil contaminated mesocosms. Bioresource Technology 56:257-264.
- RHYKERD, R.L. 1996.Biodegradation and volatilization of crude oil in soil. Ph.D.Dissertation, Texas A&M University.