Purpose This research aimed to study the adsorption of ammonium and nitrate by simply modifying the surface of the rice husk using slow pyrolysis and surfactants modification. Methods Rice husk biochar was prepared by slowly pyrolyzing at 500 °C, 2 h. The rice husk and its biochar were modified by cetyltrimethylammonium bromide or sodium dodecylbenzenesulfonate. FTIR, BET and zeta potential measurements were used to characterize the obtained adsorbents. Results Slow pyrolysis increased the specific surface area and decreased the surface charge of rice husk while surfactant clogged the pore but could change the charge of a surface. Adsorption of both ammonium and nitrate on rice husk, its biochar, and their modification with surfactants fitted Freundlich and Langmuir isotherms, indicating heterogeneity in adsorption. Slow pyrolysis gave the highest ammonium removal with maximum adsorption capacity of 44 mgN/g and it was a physical process. The cetyltrimethylammonium bromide modification gave a significant nitrate removal on both rice husk and its biochar with maximum adsorption of 278 and 213 mgN/g, respectively, which is higher than a commercial adsorbent. Conclusions These two modification techniques gave great adsorption enhancement with cost-effectiveness as compared to other reviewed methods which could use as a nitrogen-rich fertilizer and fertilizer retainment in crop production.

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Inorganic nitrogen fertilizers are widely and heavily used in agriculture. Leaching of these fertilizers is a cause of eutrophication in water bodies. This study examines the use of rice husk and its biochar, their efficiency in adsorption of ammonium and nitrate and the potential of using surfactants, sodium dodecyl benzenesulfonate (SDBS) and cetyl trimethyl ammonium bromide (CTAB), to increase adsorption. Physical and chemical properties of adsorbents were examined through BET, SEM-EDX, and CEC value, respectively. The equilibrium batch adsorption was conducted. The result showed that rice husk was lower in surface area, total pore volume, pore diameter, silica and oxygen content, and CEC value as compared to biochar. Rice husk adsorbed nitrate well while rice husk biochar adsorbed ammonium ions better. The adsorption patterns of both ammonium and nitrate were well explained by Freundlich’s isotherm and are primarily attributed to chemical charge sorption. Both adsorbents could adsorb surfactants through Van der Waals forces between the long chain of surfactant and organic fraction on the surface of rice husks, exposing the charging head for ionic pollutant adsorption. Either SDBS or CTAB-modified rice husk and its biochar could enhance the adsorption of ammonium and nitrate.

Knowledge of the various microcomponents of residential water consumption can play an essential role in setting effective water supply plans and policies. However, there is insufficient data regarding the microcomponents of domestic water use (toilet, laundry, bath, and kitchen) in developing countries. This study measured the microcomponents of residential water use in Chiang Mai and Khon Kaen, Thailand, using a small accumulative water meter attached directly to each household tap. In addition, residents were surveyed to obtain information about income, home bathing facilities, and laundering methods. Results showed water consumption per capita for every use to be distributed lognormally in Chiang Mai and Khon Kaen. Water consumption for toilet use was higher in Chiang Mai than in Khon Kaen, but the study found little difference between the two cities in other microcomponents of residential water consumption. In this research, historical differences in the cities' water resources appeared to have no effect on residential water consumption.