Abstract
Shortcomings of individual biochar or microbial technologies often exist in heavy metal removal from wastewater and may be circumvented by coupled use of biochar and microorganisms. In this study, Bacillus subtilis and each of three biochars of different origins (corn stalk, peanut shell, and pine wood) were coupled forming composite systems to treat a cadmium (Cd, 50 mg/L) wastewater formulated with CdCl2 in batch tests. Biochar in composite system enhanced the activity and Cd adsorption of B. subtilis. Compared with single systems with Cd removal up to 33%, the composite system with corn stalk biochar showed up to 62% Cd removal, which was greater than the sum of respective single B. subtilis and biochar systems. Further analysis showed that the removal of Cd by the corn stalk composite system could be considered to consist of three successive stages, that is, the biochar-dominant adsorption stage, the B. subtilis-dominant adsorption stage, and the final biofilm formation stage. The final stage may have provided the composite system with the ability to achieve prolonged steady removal of Cd. The biochar-microorganism composite system shows a promising application for heavy metal wastewater treatment.
Highlights
Heavy metals can destroy the community structure of the benthos in natural ecosystems and thereby seriously endanger ecosystems
C0 where qe is the equilibrium adsorption; V is the volume of solution (L); M is the amount of biochar added (g); R is the removal rate of Cd; C0 is the initial Cd concentration in the solution; and C is the Cd concentration in the solution after adsorption
According to the method in the previous studies (Tao et al ; Wang et al ), the B. subtilis-Cd adsorbed biochar was placed into glutaraldehyde (2.5%) to fix at 4 C for 24 h
Summary
Heavy metals can destroy the community structure of the benthos in natural ecosystems and thereby seriously endanger ecosystems. Organisms can accumulate heavy metals, posing risks to the health of other members in the food chain including humans (Tan et al ). Cadmium (Cd) has the highest potential ecological risk. Cd in the environment comes from the use of various chemicals, such as pesticides, chemical fertilizers, and biological raw materials (e.g., Nogawa et al ). Another source of Cd is from wastewater treatment plant (WWTP). The US Environmental Protection Agency (EPA) has established the maximum contaminant level (MCL) of 0.005 mg/L for Cd drinking water The World Health Organization (WHO) established a guideline of 0.003 mg/L for lifetime consumption (http:// www.who.int/water_sanitation_health/dwq/chemicals/ cadmium.pdf). As current WWTP is not capable of effectively removing Cd from wastewater, there is a need to develop a long-term and steady Cd removal method
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