Competitive adsorption behaviour and mechanisms of cadmium, nickel and ammonium from aqueous solution by fresh and ageing rice straw biochars.

In this study, competitive adsorption behaviour and mechanisms of Cd2+, Ni2+ and NH4+ by fresh and artificially ageing biochars produced from rice straw at 400 and 700 °C (RB400, RB700, HRB400 and HRB700) were investigated. Cd2+ competed with Ni2+ and NH4+ for the overlapped adsorption sites on the biochars. For Cd2+ and Ni2+ adsorption, cation exchange (Qci) and mineral co-precipitation (Qcp) were the primary mechanisms for the low-temperature and high-temperature biochars, respectively. However, the other potential mechanisms (Qco) made the greatest contributions to NH4+ adsorption (>60%). Cd2+ and Ni2+ competition increased the proportions of mineral co-precipitation (Qcp) and other potential mechanisms (Qco) but decreased that of cation exchange (Qci) mechanism. Biochar ageing increased the contribution of surface complexation (Qcf) mechanism, especially for the low-temperature biochars. This study indicated that biochar aging and types and states of adsorbates should be considered when biochars were applied to remove contaminants.

Quantitative mechanisms of cadmium adsorption on rice straw- and swine manure-derived biochars.

We quantified and investigated mechanisms for Cd2+ adsorption on biochars produced from plant residual and animal waste at various temperatures. Ten biochars were produced by pyrolysis of rice straw (RB) and swine manure (SB) at 300-700 °C and characterized. The Cd2+ adsorption isotherms, adsorption kinetics, and desorption characteristics were studied via a series of batch experiments, and Cd2+-loaded biochars were analyzed by SEM-EDS and XRD. The total Cd2+ adsorption capacity (Qc) increased with pyrolysis temperature for both biochars, however, rice straw-derived biochars had greater Qc than swine manure-derived biochars; hence, the biochar derived from rice straw at 700 °C (RB700) had the largest Qc, 64.4 mg g-1, of all studied biochars. Cadmium adsorption mechanisms in this study involved precipitation with minerals (Qcp), cation exchange (Qci), complexation with surface functional groups (Qco), and Cd-π interactions (Qcπ). Both the pyrolysis temperature and feedstock affected the quantitative contributions of the various adsorption mechanisms. The relative percent contributions to Qc for Cd2+ adsorption by RB and SB were 32.9-72.9% and 35.0-72.5% for Qcp, 21.7-50.9% and 20.4-43.3% for Qci, 2.2-14.8% and 1.4-18.8% for Qco, and 1.4-3.1% and 3.0-5.8% for Qcπ, respectively. For biochars produced at higher pyrolysis temperatures, the contributions of Qcp and Qcπ to adsorption increased, while the contributions of Qci and Qco decreased. Generally, Qcp dominated Cd2+ adsorption by high-temperature biochars (700 °C) (accounting for approximately 73% of Qc), and Qci was the most prominent mechanism for low-temperature biochars (400 °C) (accounting for 43.3-50.9% of Qc). Results suggested that biochar derived from rice straw is a promising adsorbent for the Cd2+ removal from wastewater and that the low-temperature biochars may outperform the high-temperature biochars for Cd2+ immobilization in acidic water or soils.

Major inducing factors of hypertensive complications and the interventions required to reduce their prevalence: an epidemiological study of hypertension in a rural population in China.

BACKGROUND: The complications of hypertension cause severe health problems in rural areas in China. We (i) screened the major factors inducing hypertensive complications and provided intervention measures; and (ii) verified the efficacy of the New Rural Cooperative Medical Scheme (NRCMS; a medical insurance scheme for rural residents) for hypertension management. METHODS: A survey was conducted in the villages of Yunnan (an underdeveloped province in southwest China). The NRCMS was initiated there in 2005. Data were collected through questionnaires, physical examination, electrocardiography, as well as blood and urine tests. To detect factors inducing hypertension complications, a generalized estimating equations model was developed. Multivariable logistic regression was used to analyze influencing factors for hypertension control. RESULTS: Poor management of hypertension was observed in women. Being female, old, poorly educated, a smoker, ignorant of the dangerousness of hypertension, and having uncontrolled hypertension made patients more prone to hypertension complications. Combination therapy with ≥ 2 drugs helped control hypertension, but most rural patients disliked multidrug therapy because they considered it to be expensive and inconvenient. The NRCMS contributed little to reduce the prevalence of complications and improve control of hypertension. CONCLUSIONS: The present study suggested that the NRCMS needs to be reformed to concentrate on early intervention in hypertension and to concentrate on women. To increase hypertension control in rural areas in China, compound products containing effective and inexpensive drugs (and not multidrug therapy) are needed.