Bed Irrigation Research Articles

Biofiltration of air contaminated with toluene on a compost-based bed

Many studies have focused on problems created by emissions to the atmosphere of gaseous effluents containing volatile organic compounds (VOCs). Over the more recent decades, such studies have led to the development of various bioreactors such as the bioscrubber, the biotrickling filter and the biofilter. This paper presents the results of a study on the biofiltration of airborne toluene, the biofilter employed being operated at the laboratory-scale for a continuous period of 3 months. The focus of this particular study has been the development of a new compost-based filter-bed material, which consists of an association between matured compost and a proprietary organic binder that is intended to prolong the period of the bed's efficient operations. No inoculum was added to the filter-bed material. During the experimental program, the performance of two different bed irrigation solutions was examined, the most effective nutrient supply solution then being used, along with toluene input levels varying from 0.6–2.6 g/m 3, and toluene polluted air flow rates ranging from 0.4–1 m 3/h, equivalent to empty bed residence times of 65–165 s. The results of this program have demonstrated removal efficiencies approaching 95%, while maximum elimination capacities of 55 g/m 3 h, for an inlet load of 65 g/m 3 h, have been achieved, supporting the view that the compost-based filter material tested in this work functions as a promising biofilter medium in this application. Finally, in order to present the biofilter performance observed under the best operating conditions, a simplified representation based on Ottengraf's model has been developed from the experimental results and is included here.

Sodicity v. yield decline functions for a Vertisol (Grey Vertosol) under border check and raised bed irrigation

The grain yields of 2 soybean crops and a canola crop were related to topsoil and subsoil properties that are known to affect soil aggregate stability in water. A broad range of soil conditions was produced by applying gypsum and lime at various rates to a Vertisol that was naturally sodic throughout the soil profile. The observations were made under both ‘border check’ and ‘raised bed’ irrigation. Soil factors that influence dispersibility and crop growth were considered as part of a stepwise regression analysis. For the 2 soybean crops under border check irrigation, surface exchangeable sodium percentage (ESP) explained 72 and 63%, respectively, of the grain yield variation. For the canola crop that followed, a combination of pH, ESP and electrical conductivity (in that order) explained 75% of the variation in grain yield. Grain yields for the 3 crops declined as the soil became more sodic, particularly on the flat border check area. For soybeans (flat area), the critical values of ESP at which surface sodicity caused a 50% yield decline (ESP50) were strongly influenced by the post-planting climatic conditions. When there was heavy rain just after germination of the soybean seedlings, the ESP50 value was 8.6. The more sodic areas developed a thick crust that impeded seedling emergence. However, in the following year, when conditions remained dry after planting, the ESP50 value was 10.7. Under bed irrigation, the influence of ESP on yield was only minor after the first year of cropping. There was evidence of soil structure improvement from salt that was deposited in the beds via the irrigation water. Subsoil chemical properties that affect structural stability had more of an influence on crop yield under beds than under the flat areas.

Intraoperative saline and gemcitabine irrigation improves tumour control in human squamous cell carcinoma-contaminated surgical wounds.

The cure rates for advanced head and neck cancer patients have not changed substantially in the past few decades. Most disease recurrences are local or regional and are likely due to residual microscopic disease or intraoperative wound contamination. We developed a murine model of wound implantation with microscopic disease to assess the efficiency of tumour development and used this model to evaluate the effects on tumour development of surgical bed irrigation with three different solutions. Nonobese diabetic/severe combined immunodeficient mice were transplanted with the University of Michigan squamous cell carcinoma-22B cells derived from a human squamous cell carcinoma of the hypopharynx. Two 1-cm surgical wounds were created on the backs of 20 mice and then instilled with a known quantity of tumour cells. The minimum necessary dose to reliably result in tumour growth was then determined. Forty mice were then inoculated with this minimum tumour concentration. Ten of these mice had their incisions closed immediately and were kept as controls. Ten of the mice had their wounds irrigated with 5 cc of water and then closed, 10 had their wounds irrigated with 5 cc of saline and then closed, and 10 had their wounds irrigated with 5 cc of 1-mM gemcitabine, a nonirritating chemotherapy drug with activity in human head and neck cancers. The mice were then observed for the development of palpable tumours. We were unable to successfully grow tumours in any wounds that were seeded with less than 2.5 x 10(6) cells. After exposure to 2.5 x 10(6) cells, seven of eight surgical beds developed palpable tumours. This was then taken as our standard inoculation dose. All of the study mice wounds healed rapidly irrespective of irrigation solution. At postoperative day 17, 70% of the controls had evident tumour growth, whereas only 15% of the water irrigation group (p < .0005), 0% of the saline irrigation group (p < .0001), and 0% (p < .0001) of the gemcitabine irrigation group had developed tumours. By day 24, the disease recurrence rates in the water irrigation group no longer differed from controls, whereas the lower incidence of tumour recurrence in the gemcitabine and saline irrigation groups persisted. On day 56, 80% of the control mice and 75% of the water-irrigated mice group had developed palpable tumours. In the saline and gemcitabine groups, however, only 40% (p < .01) and 35% (p < .004), respectively, had evident tumours. In a xenograft model of tumour-cell wound contamination, irrigation with saline, water, or gemcitabine delayed tumour development. Irrigation with gemcitabine or saline improved rates of long-term disease control. Gemcitabine irrigation did not affect wound healing and was free of local complications.

Water management in raised bed systems: a case study from the Chao Phraya delta, Thailand

Agricultural diversification is a major trend in Asian rice-based systems. In lowlands, however, soil and water conditions are mostly suitable for rice cultivation and the development of raised beds is often required to accommodate vegetables or fruit trees. Raised bed systems go together with specific techniques of water management, both at the polder level (between the plots and the canals) and at the plot level (bed irrigation). Details of this management in the Chao Phraya Delta are given for three different crops: mango, grapes and asparagus and differences are explained. The water balance over 1 year is specified, showing the impact of seepage and estimating water requirements. Water quality is shown to be a major issue.

Sorption of radon-222 to natural sediments

The sorption of Rn to sediments was investigated, since this may affect the use of porewater Rn profiles for estimating bed irrigation rates. Batch experiments showed that Rn has an organic carbon normalized sediment-water partition coefficient ( K oc ) of 21.1 ± 2.8 for a Boston Harbor sediment, 25.3 ± 2.1 for a Charles River sediment, and 22.4 ± 2.0 for a Buzzards Bay sediment. These values are in close agreement with predictions using the octanol-water partition coefficient ( K ow ) which we measured to be 32.4 ± 1.5. Temperature and ionic strength effects on K oc were estimated to be small. Given rapid sorption kinetics, we suggest that slurry stripping techniques used by many investigators to measure 222Rn in sediment samples collect both sorbed and dissolved radon. Sorption effects were included in a transport model to obtain revised estimates of irrigation rates from existing literature profiles. Irrigation rates had to be increased over previously reported values in proportion to the sediment organic matter content.