A significant quantity of biologically produced sulfur (BPS) is generated as a by-product of chemical and biological desulfurization processes applied to landfill gas treatment. The beneficial upcycling of BPS has seen limited use in the environmental context. The effectiveness and underlying mechanism of BPS as an adsorbent for removing Hg²⁺ from both solution and wastewater were elucidated based on experiments encompassing surface characterization, adsorption isotherms, kinetics, and thermodynamics. The BPS exhibited remarkable efficacy in removing Hg²⁺ from solution, with the Langmuir model accurately describing the adsorption process and showing a maximum adsorption capacity of 244 mg g⁻¹. Surface analysis through X-ray photoelectron spectroscopy and scanning electron microscopy revealed that Hg²⁺ complexed with sulfide on BPS surfaces, forming stable HgS. The adsorbed Hg was strongly retained in BPS, with less than 0.2% of the adsorbed Hg desorbed by strong acids. Adsorption kinetics followed the double-exponential first-order model, showing an initial rapid adsorption phase wherein 75% of the initial Hg²⁺ was removed within 5 min, followed by a slower adsorption rate. The thermodynamic parameters suggested that adsorption of Hg²⁺ by BPS was a spontaneous and endothermic process. Additionally, BPS effectively removed Hg²⁺ from wastewater, showing preference for Hg over other co-existing metals. These findings underscore the potential of BPS as an effective adsorbent for Hg²⁺ removal from wastewater.

The combination of lime immobilization of metals and soil dressing has been a prevalent practice in Korea for remediating metal-contaminated arable soils. However, there have been limited reports on whether this method effectively sustains soil health after remediation, particularly in arable soils. This study undertook a comparative assessment of the soil health index (SHI) across metal-contaminated arable lands, arable soils remediated with lime immobilization and soil dressing, and uncontaminated soils. A total 389 soil samples were collected from these sites and analyzed for nineteen indicators encompassing physical, chemical, and biological properties. To assess soil health, these indicators were screened using principal component analysis, yielding five minimum data set (MDS) indicators: total nitrogen, clay content, dehydrogenase activity, bacterial colony-forming units, and available phosphorus. Among these MDS indicators, total nitrogen exhibited the highest value as the principal component contributing to soil health assessment. Scores of the MDS indicators exhibited significant correlation with those of total data set indicators, affirming the appropriateness of the soil health assessment adopted in this study. The SHI of the remediated arable soils (0.48) surpassed those of the contaminated soils (0.47) and were statistically comparable to those of the uncontaminated forest (0.51) and upland (0.51) soils. The health of the contaminated soils demonstrated a high dependence on soil properties rather than metal concentrations. These findings underscore the robustness of the combined immobilization and soil dressing method for sustaining the health of contaminated arable soils post-remediation.

Soil bulk density and three-phase composition are critical physical indicators for evaluating soil health and supporting sustainable soil management. In-situ measurement of these properties helps diagnose field-related constraints affecting productivity, such as poor drainage, compaction, aeration, and drought stress. While the oven-dry gravimetric method (OG) is the standard for measuring these parameters, its application in the field is constrained by time and equipment requirements. To address this, a simple field volumetric method (FV) was developed and validated through comparative analysis with the OG method. Both methods were applied to 38 soil samples to measure bulk density and three-phase composition (solid, liquid, and gaseous). Agreement was assessed using linear regression, coefficient of variation (CV), Bland-Altman plots, and Cronbach's alpha. Regression results showed significant (P < 0.01) correlations between methods, with r 2 values of 0.89-0.91 and standard errors ranging from 0.05 to 3.92. The solid phase showed the highest compatibility among the three-phase composition. CVs ranged from 4.7-17.3 for FV and 3.5-15.2 for OG, but differences were not statistically significant. Most values fell within the 95% limits of agreement in Bland-Altman analysis. Cronbach's alpha values higher than 0.7 (0.95-0.97) indicated excellent internal consistency across parameters. These findings demonstrate that the FV method provides a reliable and efficient alternative for rapid field assessment of soil bulk density and three-phase composition.

Aquaponics (AP) is the combination of aquaculture and hydroponic systems, developed based on waste to wealth theory. This study compared the plant growth and overall productivity of an aquaponic system (AP) with a controlled hydroponic system (HP) to assess the AP system’s performance and identification of the performance-limiting factors. This comparative study spanned over a 35-day period, supported by batch tests for the nutrient accumulation rate in plants and the NH₄⁺-N excretion rate by fish as a baseline for the system design. HP performed better in terms of plant growth, showing a mean plant fresh weight (g) of 165.6 ± 3.01 while AP showed 147.0 ± 4.6. Nutrient accumulation was better in HP for K and P; however, Ca²⁺, Mg²⁺, and Fe accumulation was higher in AP plants. The AP system supported a better fish growth of 31.95 ± 3.21% (FCR 1.29 ± 0.1, SGR 0.79 ± 0.06, and PER 2.24 ± 0.18) and a moderate plant biomass production. Further system design modifications and integrations are required to optimize the nutrient availability and sustainability of the AP systems.