The-Proof-of-Concept of Biochar Floating Cover Influence on Water pH

Abstract

Studies have shown that biochar has the potential to remove organic and inorganic contaminants from wastewater. pH is known to have a crucial role in the transformation of pollutants. In this research, we explore the feasibility of using biochars properties to control the pH near the water-air interface, so the gaseous emissions from water (or wastewater) could be mitigated. This study aimed to test the effects of a thin layer biochar addition on the spatial and temporal variation of water pH. Two types of biochar and water were tested. Highly alkaline porous (HAP; pH 9.2) biochars made of corn stover and red oak (RO; pH 7.5) were applied surficially to tap (pH 9.5) and deionized water (DI) (pH 5.4). The spatial pH of solutions was measured every 1 mm of depth on days 0, 2, and 4 after biochar application. The results showed that HAP biochar increased the pH of both tap and DI water, while RO decreased tap water pH and increased DI water pH. On day 0, there was no effect on tap water pH, while a pH change in DI water was observed due to its lower buffer capacity. In addition, the pH (temporal) migration from topically applied biochar into an aqueous solution was visualized using a colorimetric pH indicator and corn starch to increase viscosity (to prevent biochars from sinking). The results prove that the surficial application of biochar to water was able to change both the pH near the water-air interface and the pH of the solution with time. The pH change was dependent on the biochar pH and water buffer capacity. These results warrant further research into the floatability of biochars and into designing biochars with specific pH, which could be a factor influencing gaseous emissions from liquids that are sensitive to pH.

Mitigation of Gaseous Emissions from Swine Manure with the Surficial Application of Biochars

“…Ayiania et al studied that the mechanism of H2S sorption is driven by the size of biochar pores [49]. However, our experiments showed that HAP biochar with pH=9.2 and larger pores [34] performed less H2S reduction in comparison with RO over all three trials. It should be mentioned that FTIR spectra (Figure 7) showed that RO had higher peaks in OH and COOstretching.…”

“…Fixed C content was estimated by subtracting percentages of moisture, volatile matter, and ash content from the sample [41]. Results of the elemental analyses, moisture/fixed C, volatile matter, and pH are summarized elsewhere [34]. In addition, a solid addition method was used to analyze the zero point charge (ZPC) of biochars.…”

“…Pore images of biochars were taken using the scanning electron microscopy (SEM) method (FEI Quanta 250 FE-SEM) [39]. Results of SEM analyses are summarized elsewhere [34].…”

“…Another property of HAP biochar that made it sink in manure could be high ash content in comparison with RO biochar. In addition, the differences in pore size associated with HAP and RO biochars (visible in SEM images, [34]) could also affect the liquid penetration. Another parameter that could affect biochar floating on top of manure is the solid content in manure.…”

“…Most recently, we reported on the spatial and temporal effects on the pH in the liquid-air interface after the surficial application of HAP and RO biochars to water [34] and swine manure [35]. This research reports on the next logical step, i.e., evaluation of the mitigation effect of biochars on gaseous emissions from swine manure.…”