Tian C. Zhang

Sulfur:limestone autotrophic denitrification processes for treatment of nitrate-contaminated water: batch experiments

Abstract In this study, an innovative process of using sulfur:limestone autotrophic denitrification (SLAD) for treatment of nitrate-contaminated surface or wastewater was put forward. The feasibility of this SLAD process was evaluated using lab-scale batch reactors operated under both aerobic and anaerobic conditions. Autotrophic denitrification occurred in batch reactors spiked with sulfur:limestone (S:L) under either aerobic or anaerobic conditions at both high (ca. 300–500xa0mgxa0NO3−–N/l) and low (ca. 30xa0mgxa0NO3−–N/l) initial nitrate concentrations. Nitrate–nitrogen removal increased with the addition of granular sulfur and limestone, while the addition of a seed of autotrophic denitrifiers into the batch reactors accelerated nitrate removal. Limestone was necessary to control the pH within the reactors. The optimum sulfur:limestone ratio was 3:1 (v/v) and the extent and rate of nitrate removal depended on the alkalinity within SLAD batch reactors. Nitrate removal efficiency, sulfate production and biomass accumulation were usually higher under aerobic conditions than under anaerobic conditions. Bacterial counts signified that both autotrophic denitrificans and nondenitrifying bacteria such as Thiobacillus thiooxidans were involved in the process under aerobic conditions. The SLAD process may be a replacement for heterotrophic denitrification in pond systems such as constructed wetlands or stabilization ponds due to the fact that no organic carbon source is needed in the SLAD process and that autotrophic denitrificans exist widely in natural sediments or soil.

An innovative electro-corrosion recess creation technique for improved microelectrode fabrication.

A new and simple electrochemical (corrosion) method for recess creation for the fabrication of metal and metal-metal oxide microelectrodes has been developed. Controlled recess was created in low melting point alloy (LMA)-filled micropipettes using slightly acidic 1-3 M ZnCl2 as the electro-corrosion solution. The current was applied from a 3 V DC source. The recess length in the LMA-filled micropipette can be manipulated as needed for a specific microelectrode by varying the electro-corrosion time. The present method is expected to make microelectrode fabrication a less tedious process. Dissolved oxygen, oxidation-reduction potential and pH microelectrodes have been made using the present method and the microelectrode characteristics were found to be in conformity with those reported by other researchers.

Sorption of testosterone on partially-dispersed soil particles of different size fractions: Methodology and implications.

Sorption of hormones to soil particles of different size fractions (DSFs) has been studied to understand their fate and transport (F/T) in soils. Conventional studies fractionated the soil particles into DSFs by using the high speed stirring method and/or adding surfactants to fully disperse the bulk soil. However, the natural processes (e.g., soil erosion, irrigation) often are relatively mild, and many soil particles may be still in the aggregate form. In this study, a method was developed for conducting the sorption test of a representative hormone (i.e., testosterone) to bulk soils first and then analyzing the results against DSFs. Results indicated the particle size distribution (PSD) of the two representative soils tested with partially-dispersed and fully-dispersed methods was significantly different due to the attachment of clay particles on sand and silt. Testosterone was sorbed mainly by the dominant aggregates even though they might have relatively lower sorption affinity than that of clays. However, the small particles (<2000xa0nm), even with ∼5% mass of the bulk soil, contributed more than 30% of sorbed testosterone in the whole soils. The partially-dispersed soil particles of DSFs should be used to understand the transport of hormone in runoff, because using the fully-dispersed soil particles will overestimate while the whole soil method will underestimate the transport potential. With the methodology developed in this study, the sorption tests will not compromise soils original properties (e.g., aggregates) or the competition (e.g., sorption) among soil particles, and the contribution of DSFs (particularly the partially-dispersed aggregates) to the sorption of the whole soil can be determined.

Transport of manure-borne testosterone in soils affected by artificial rainfall events

Information is very limited on fate and transport of steroidal hormones in soils. In this study, the rainfall simulation tests were conducted with a soil slab reactor to investigate the transport of manure-borne testosterone in a silty-clay loam soil under six controllable operation conditions (i.e., three rainfall intensities and two tillage practices). The properties [e.g., rainwater volume, particle size distribution (PSD)] of the slurry samples collected in runoff and leachate at different time intervals were measured; their correlation with the distribution of testosterone among runoff, leachate and soil matrix was analyzed. The results indicated that more than 88% of the testosterone was held by the applied manure and/or soil matrix even under the rainfall intensity of 100-year return frequency. The runoff facilitated testosterone transport through both dissolved and particle-associated phases, with the corresponding mass ratio being ∼7 to 3. Soil particles collected through runoff were mainly silt-sized aggregates (STA) and clays, indicating the necessity of using partially-dispersed soil particles as testing materials to conduct batch tests (e.g., sorption/desorption). No testosterone was detected at the soil depth >20 cm or in the leachate samples, indicating that transport of testosterone through the soil is very slow when there is no preferential flow. Tillage practice could impede the transport of testosterone in runoff. For the first time, results and the methodologies of this study allow one to quantify the hormone distribution among runoff, leachate and soil matrix at the same time and to obtain a comprehensive picture of the F/T of manure-borne testosterone in soil-water environments.