Enhancing chemical phosphorus precipitation from tapioca starch anaerobic digestion effluent in a modified pilot-scale fluidized bed reactor.

This study aimed to evaluate the possibility of P precipitation as struvite from real anaerobic digestion (AD) effluent of tapioca starch processing. The results showed that at a pH of 9, and without Mg:P molar adjustment, P recovery was at 85%. The percentage of P recovery was increased to 90% and P contained in precipitates was at 11.80-14.70 wt% P, which is higher than commercial single superphosphate fertilizer (SSP, 18-22 wt% P2O5). This was achieved by controlling mixing at 200-400 rpm and upflow velocity at 50-200 cm min-1 inside a fluidized bed reactor (FBR). Based on SEM-EDX, powder XRD, phase identification by profile matching, and FT-IR analysis, the results demonstrated that recovered precipitates formed struvite predominantly. In addition, results of the woodchip ash additions and the one-way ANOVA based-RSM analysis revealed that mixing, the solution pH, and the woodchip ash intensely affected P recovery with the optimum condition found at 400 rpm, pH9, 4 g L-1, respectively. Ash addition enhanced P recovery efficiency but decreased the product's purity. Total costs of P recovery varied considerably from 0.28 to 7.82 USD∙(kg P)-1 depending on chemical consumption and %P content in recovered products. Moreover, the total cost was reduced by 57% from 7.82 USD∙(kg P)-1 (profit margin: -4.30 to -2.82) by a single mixing operation to 3.35 USD∙(kg P)-1 (profit margin: +0.17 to +1.65) employing coupling effect of mixing and Vup. The results indicate that P recovery from tapioca starch AD effluent not only provides a good-quality alternative slow-release P fertilizer, but also helps to curtail environmental problems due to excessive P and nitrogen discharge. These findings also demonstrate the ways of recovering nutrients from an abundant renewable resource that are relevant to simultaneous waste utilization during pollution controls.

Application Intensity and Spatial Distribution of Three Major Herbicides from Agricultural and Nonagricultural Practices in the Central Plain of Thailand.

The herbicides glyphosate, paraquat, and 2,4-D play a significant role in Thailand. This paper is among the first study to describe the intensity of herbicide application and illustrate how the herbicides are extensively distributed over a large area through both agricultural and nonagricultural practices. Using a quick, economical, and simplified method of Material Flow Analysis together with spatial analysis, better data for the analysis of possible environmental herbicide contamination, human exposure, and related health risks for the general public and applicators can be developed. The findings from this study showed that in the study province, about 2.2 million kg of the active ingredients from the three targeted herbicides is applied annually. Pathway flow modeling with spatial analysis identified several local hotspots of concern based on the type of herbicide and crop/activity where it was used. Cassava planting was found to have the highest herbicide application activity, whereas rice cultivation was the major contributor of total herbicide mass, due to the wide area of cultivation in the province. The herbicide most likely to be applied at rates higher than recommended was 2,4-D, particularly on cassava and sugarcane farms.

Human exposure to phthalates from house dust in Bangkok, Thailand.

The study determined concentrations of and estimated human exposure to house dust-ingested phthalates from 99 homes in Bangkok, Thailand. Phthalates in dust collected using a handheld vacuum cleaner was analyzed by gas chromatography/mass spectrometry revealing a median content of 3,477 µg g-1, range 753-13,810 µg g-1, with di-2-ethylhexylphthalate (DEHP) having the highest level (median = 1,739 µg g-1, range 467-8,172 µg g-1) followed by di-iso-nonyl phthalate (DiNP) (median = 611 µg g-1, range 15.2-11,052 µg g-1). DEHP in house dust from multi-family apartments with polyvinyl (PVC) floor material (n = 34), multi-family apartments without PVC floor material (n = 55) and single family houses without PVC floor material (n = 10) was median and range 3,009 and 568-6,898; 1,479 and range 467-8,172 and 1,207 µg g-1 and 611-3518 µg g-1, respectively. At high-end house dust DEHP level, preschool children in all three types of homes were exposed above US Environment Protection Agency reference dose (20 µg g-1). The results suggest phthalate-containing house products constitute a likely major source of phthalates in indoor home environment and pose a potential health risk to residents, particularly preschool children, in Bangkok.

Integrating spatial land use analysis and mathematical material flow analysis for nutrient management: a case study of the Bang Pakong River Basin in Thailand.

Rivers in developing and emerging countries often lack good water quality. Tools to assess the water quality in rivers, including identification of possible sources of pollution, are therefore of increasing importance. The aim of this study is to apply mathematical material flow and spatial land use analyses to identify and geographically locate the main nitrogen and phosphorus sources and processes in Bang Pakong Basin (BPB). Potential measures to mitigate the nitrogen and phosphorus loads to the water system can then be efficiently evaluated. The combination of these two methods reveals the overall nutrient load as well as local "hot spots." This allows possible mitigation measures to be discussed with regard to their spatial location. This approach goes beyond previous work in which mathematical material flow analysis was shown to be a useful tool to investigate sources of nutrients regardless of their location. The results show that the main sources contributing nutrients to waterways are aquaculture, such as shrimp, tilapia, catfish, and sea bass farming, as well as rice paddies along the main river. Additional sources contributing nutrients to this basin are field crops, livestock, aquaculture, households, and industry. High levels of nutrient inflows come from feeds and fertilizers through aquaculture and rice cultivation. The excess nutrients run into the waterways by direct discharge from aquaculture and runoff processes from rice paddies. Scenario analysis shows that management practices for aquaculture, rice, pig, and poultry farming are key drivers for reducing nutrients in the BPB.