Theoretical results:
- Assessment of surface water quality of the Red River flowing from upstream through the downstream Thai Binh - Nam Dinh showed that residues of the herbicide Glyphosate and its metabolites were detected simultaneously in the river water with low concentration. The content of these substances varies considerably, depending on the time, area and weather of sampling, the hydrological features of the flow, and especially the control of the discharge sources into the river. The surface water environment in the areas is polluted mostly by organic substances and microorganisms exceeding the allowable threshold.
- Biochars derived from agricultural by-products including coir and rice husks have been successfully produced in large quantities, homogeneously after calcination, and then activated by different conditions: H2O, HNO3 and NaOH 10% and 25% at room temperature and high temperature (90oC). The biochars had a high specific surface area of 329.71 m2/g and 364.22 m2/g for coir fiber biochar (BC1) and rice husk biochar (BC2), respectively. All biochars have a micro and medium structure but in different amounts. The biochar obtained in this study may have a high adsorption capacity for small to large molecules. Both BC1 and BC2 showed good adsorption capacity for Glyphosate. However, BC2 has better adsorption performance than BC1. In addition, the study also successfully produced biochar from rice husks impregnated with TiO2 which exhibits good photocatalytic properties and effectively removes glyphosate from aqueous solution.
- The adsorption column was 2 mm thick glass tubes with an inner diameter of 2.8 cm and an effective length of 53 cm. One end of each glass tube is welded with a threaded mouth (outer diameter 4.5 cm, inner diameter 3 cm) with a plastic cap for adding materials to the tube and removing the material as well as helping to clean the tube after each experiment easily and effectively. The threaded mouth of the column also ensures that the liquid in the column cannot leak to the outside, facilitating the study of the effects of a large flow range on the column performance. The plastic cap is connected to an outlet pipe with an outer diameter of 5 mm and an inner diameter of 3 mm serving the connection to the water supply pipe. The other end of the glass tube is sealed with a hole disc and welded with a valve (outlet diameter 8 mm, inner diameter 5 mm). The perforated glass disc helps to the packing materials in the tube while ensuring efficient drainage of water out of the tube through the valve. The entire column materials including quartz, glass and Teflon resin which have good chemical inertness and can use for the study of many types of pollutants as well as under harsh experimental conditions (such as very low or very high pH).
Applied results:
- Biochar from rice husk and coir both have good Glyphosate adsorption capacity compared with different adsorbents, such as bamboo activated carbon, pea pods, modified clay sphere, and biochar wakame-derived activation. On the other hand, the biochar made in this study with a particle size of 1 – 2 mm for coir and 5 mm for rice husk is more eco-friendly and cost-effective than other adsorbents. Firstly, the granular nature of the adsorbent is useful because it can be easily separated after filtration and settling without generating sludge. Second, in terms of recycling, using agricultural by-products allows agricultural waste to be more valued to reduce environmental risks.
- The adsorption column system consists of 3 quartz columns connected in series representing one pre-column and two main treatment column. The system is directly connected to a dual-channel peristaltic pump with total capacity of 750 to 3000 mL/h. This system allows the treatment of two parallel systems at the same time with different material conditions and different pollutant sources, as well as allowing direct treatment of river water and no pre-filtration or pre-treatment is required. | 
