R. W. Weaver

Improvement of domestic wastewater quality by subsurface flow constructed wetlands.

Abstract A large proportion of households throughout the world and approximately 25% of the households in the US use on-site wastewater disposal systems. Subsurface flow constructed wetlands are gaining popularity as a reduced cost and low-maintenance technology for on-site treatment of septic effluents. Constructed wetlands from residences at eight locations in Texas have been used for the past 2–4 years to determine their effectiveness in improving the quality of septic effluent passing through them. Influent and effluent samples were collected once every month over a period of one year from each location and analyzed to determine the reduction in concentrations of biological oxygen demand (BOD 5 ), total suspended solids (TSS), volatile suspended solids (VSS), ammonium-N (NH 4 + -N), phosphorus, total and fecal coliform bacteria. Results of these investigations indicate that the organic load, fecal coliform populations and the N and P concentrations of the septic water decreased considerably by passing through the wetlands. Constructed wetlands reduced BOD 5 of septic water by 80–90% which provided for feasible disinfection by chlorination. Reduction in populations of fecal coliforms varied but generally, populations were reduced by 90–99%. Chlorination further reduced populations of fecal coliforms to less than 2 cfu 100 ml −1 . Constructed wetlands provided an effective method for secondary treatment of on-site domestic wastewater.

Carbon and nitrogen mineralization from cowpea plants part decomposing in moist and in repeatedly dried and wetted soil

from 46% of initial plant N in moist -oil to 29% in repeatedly dried and wetted soil at 68 days. Carbon and N mineralization from cowpea were linearly related after an initial phase of rapid C loss. With repeated drying and wetting, a greater amount of N remained in undecomposed plant material, that was retrieved periodically during incubation. Repeated drying and wetting of the soil appeared to increase the resistance of certain N compounds of the plant to microbial decomposition. Further, repeated drying and wetting of the soil severely inhibited growth and/or activity of nitrifiers. Periodic drying of the soil as occurs in the field will reduce N mineralization from legume green manures compared to the decomposition in continuously moist soil, but may contribute to long-term N fertility by increasing soil organic N content.

A new technique for most-probable-number counts of Rhizobia

SummaryMPN (most-probable-number) counts of rhizobia by using legumes grown in plastic pouches were essentially equal to pour-plate counts. By using plastic pouches, 60 growth units could be placed in 684 cm2 of bench space, and only 20 minutes were required to prepare and seed 60 plastic pouches for inoculations.

Impact of bulking agents, forced aeration, and tillage on remediation of oil-contaminated soil

Abstract Bioremediation is a relatively new technology used to remediate contaminated soil that involves oil degrading microorganisms. Adequate aeration is essential for oil degrading microorganisms to be active. Methods of promoting aeration are tillage, pumping air into the soil, and adding bulking agents to increase porosity. More knowledge is needed regarding the interaction between bulking agents and other technologies in enhancing aeration for bioremediation of oil-contaminated soil. An experiment was undertaken using oil-contaminated soil from an oil production site in east Texas to evaluate different methods to promote aeration. Each treatment contained 10% total petroleum hydrocarbons (TPH) on a dry weight basis. Treatments were bulking agents (non-bulked control, chopped bermudagrass hay, sawdust, and vermiculite) and aeration (static, tillage, and forced aeration). Treatments were arranged in a 4 × 3 factorial with three replications in a completely randomized design. Sawdust and vermiculite were added at equal volumes with the contaminated soil and chopped bermudagrass hay at a ratio of 1 volume of hay to 2 volumes of contaminated soil. Experimental units were 100 1 barrels open at the top. The TPH content was determined every 6 weeks during a 30 week period. During this time the TPH content decreased in all treatments. Bulked soils showed a more rapid reduction in TPH compared to the non-bulked control. Tilling increased the rate and extent of remediation more than soil receiving forced aeration or left static. The most rapid rate of remediation occurred during the first 12 weeks from the tilled-hay treatment, where the TPH decreased 82%. The slowest remediation rate occurred in the non-bulked-static treatment where the TPH content decreased 33% in 12 weeks. By week 30 the TPH content of the treatments ranged from 90% degraded in the tilled-hay and tilled-vermiculite treatments to 77% degraded for the non-bulked-static treatment. Tillage and adding bulking agents enhanced remediation of oil-contaminated soil.

Influence of salinity on bioremediation of oil in soil.

Spills from oil production and processing result in soils being contaminated with oil and salt. The effect of NaCl on degradation of oil in a sandy-clay loam and a clay loam soil was determined. Soils were treated with 50 g kg(-1) non-detergent motor oil (30 SAE). Salt treatments included NaCl amendments to adjust the soil solution electrical conductivities to 40, 120, and 200 dS m(-1). Soils were amended with nutrients and incubated at 25 degrees C. Oil degradation was estimated from the quantities of CO(2) evolved and from gravimetric determinations of remaining oil. Salt concentrations of 200 dS m(-1) in oil amended soils resulted in a decrease in oil mineralized by 44% for a clay loam and 20% for a sandy-clay loam soil. A salt concentration of 40 dS m(-1) reduced oil mineralization by about 10% in both soils. Oil mineralized in the oil amended clay-loam soil was 2-3 times greater than for comparable treatments of the sandy-clay loam soil. Amending the sandy-clay loam soil with 5% by weight of the clay-loam soil enhanced oil mineralization by 40%. Removal of salts from oil and salt contaminated soils before undertaking bioremediation may reduce the time required for bioremediation.

OIL BIOREMEDIATION IN SALT MARSH MESOCOSMS AS INFLUENCED BY N AND P FERTILIZATION, FLOODING, AND SEASON

Bioremediation of crude oil in salt marsh mesocosms growingSpartina alterniflora was investigated during winter and summer to determine the influence of nitrogen (N) and phosphorus (P) fertilization, flooding, and season. Fertilization with urea and ammonium (NH4+) applied at 75 or 150 kg N ha−1 with or without P did not significantly (p=0.05) increase oil or hydrocarbon degradation in continuously flooded mesocosms over an 82 day period during winter (temperature range of 17 to 30 °C). Phosphorus applied at 40 kg P ha−1 significantly (p = 0.05) increased oil and hydrocarbon degradation. Nitrate (NO3−) ) added alone did not increase oil or hydrocarbon degradation, but when added with P, it significantly (p = 0.05) increased degradation above that for P alone. Up to 70% of applied oil and 75% of applied hydrocarbons were degraded in P supplemented treatments. Inipol, an oleophilic fertilizer containing N, P, and a dispersant, significantly increased oil and hydrocarbon degradation. During a 40 day summer experiment (temperature range of 27–42 °C), N and P fertilization did not increase oil or hydrocarbon degradation. For continuously flooded treatments, 72% of applied hydrocarbons were degraded while 51% were degraded in alternately flooded treatments. Mesocosms provided conditions suitable for quantitative recovery of oil and results indicated that N and P fertilization, flooding, and season interacted to influence oil bioremediation. Even under the most favorable conditions, more than 1 month was required for most of the oil to disappear.

Earthworm survival in oil contaminated soil

Earthworms are an important component of the soil biota and their response to oil pollution needs to be better understood. Laboratory investigations were undertaken to determine the concentrations of crude oil in soil that leads to death of Lumbricus terrestris and Eisenia fetida and to determine the propensity of L. terrestris to move away from contaminated soil. Clemville sandy clay loam was amended to contain maximum oil contents of 1.5 – 2.5% depending on the particular experiment. Additionally, the ability of L. terrestristo survive in bioremediated oil-contaminated soil was evaluated. An oil content of 0.5% was not harmful to survival of earthworms for 7 d but an oil concentration of 1.5% reduced survival to less than 40%. Bioremediated soil containing 1.2% oil did not reduce survival of L. terrestrisduring 10 d. Survival of L. terrestrisin unweathered oil was improved when free movement between contaminated and uncontaminated soil was possible. Casts of earthworms exposed to oil-containing soil contained 0.2% total petroleum hydrocarbons. An allowable regulatory level of 1% oil contamination in soil may not allow for survival of earthworms.

Nitrification in a zeoponic substrate.

Clinoptilolite is a zeolite mineral with high cation exchange capacity used in zeoponic substrates that have been proposed as a solid medium for growing plants or as a fertilizer material. The kinetics of nitrification has not been measured for NH4+ saturated zeoponic substrate. Experiments were conducted to evaluate the production of NO2− and NO3−, and nitrifier populations in zeoponic substrates. Small columns were filled with zeoponic substrate inoculated with a commercial inoculum or soil enrichment culture of nitrifying bacteria. In addition to column studies, a growth chamber study was conducted to evaluate the kinetics of nitrification in zeoponic substrates used to grow radishes (Raphanus sativus L.). The zeoponic substrate provided a readily available source of NH4+, and nitrifying bacteria were active in the substrate. Ammonium oxidation rates in column studies ranged from 5 to 10 μg N g−1 substrate h−1, and NO2− oxidation rates were 2 to 9.5 μg N g−1 substrate h−1. Rates determined from the growth chamber study were approximately 1.2 μg N g−1 substrate h−1. Quantities of NH4+ oxidized to NO2− and NO3− in inoculated zeoponic substrate were in excess of plant up-take. Acidification as a result of NH4+ oxidation resulted in a pH decline, and the zeoponic substrate showed limited buffering capacity.

Effect of high root temperature on Bradyrhizobium-peanut symbiosis

Three strains of Bradyrhizobium, 280A, 2209A and 32H1, that nodulated peanuts (Arachis hypogaea L.), were tested for their ability to grow and survive at elevated temperatures of up to 42°C in laboratory culture. Strain 32H1 was unable to grow at 37°C and was more sensitive to elevated temperatures than the other two strains. All three produced heat-shock proteins of molecular weights 17 kDa and 18 kDa. Two greenhouse experiments were conducted to determine the effect of high root temperature on nodulation, growth and nitrogen fixation of peanut. Two peanut varieties (Virginia cv NC7 and Spanish cv Pronto) were inoculated and exposed to root temperatures of 30°, 37° and 40°C. Nodulation and nitrogen fixation were strongly affected by root temperature but there was no variety × temperature interaction. At a constant 40°C root temperature no nodules were formed. Nodules were formed when roots were exposed to this temperature with diurnal cycling but no nitrogen fixation occurred. Highest plant dry weight, shoot nitrogen content and total nitrogen were observed at a constant root temperature of 30°C. Increasing root temperature to 37°C reduced average nitrogen content by 37% and total nitrogen by 49% but did not reduce nodulation. The symbiotic performance of the strains corresponded to their abilities to grow and survive at high temperature in culture.

Nitrogen transfer from arrowleaf clover to ryegrass in field plantings

Arrowleaf clover (Trifolium vesiculosum Savi) and annual ryegrass Lolium multiflorum Lam.) commonly are overseeded in dormant bermudagrass (Cynodon dactylon L. Pers.) sod on coastal plain soils in the southeastern United States. Two field experiments were conducted in consecutive years at different sites to estimate the amount of N transferred from the clover to the annual grass. Nitrogen treatments included 50 kg N ha-1 as 15N depleted ammonium nitrate applied in either February or April, and a check (no N applied). Three clippings were made during the cool-season from March to June. In both experiments, less than 5 kg N ha-1 were transferred from the clover to the grass. Ryegrass yields of dry matter and total N were not increased by growing with clover. Clover growth was typical for the region; average dry matter yield in pure stand was 2,615 kg ha-1 over the two-year period. Clover in mixed stand fixed between 20 and 60 kg N/ha. Less than 13% of N contained in ryegrass was transferred from arrowleaf clover to ryegrass at any clipping while clover was actively growing. The quantity of N transferred over the entire season was not statistically significant.