Comparative role of charcoal, biochar, hydrochar and modified biochar on bioavailability of heavy metal(loid)s and machine learning regression analysis in alkaline polluted soil.

Pot experiment was performed aimed to assess the comparative role of charcoal, biochar, hydrochar and thiourea-vegetable modified biochar at 1 and 2 % doses, and <1 mm particle size on the bioavailability of Cd, Pb, As, Ni, Cu and Zn, and enhance NPK, and mustard growth in a slightly alkaline polluted soil. Furthermore, machine learning method was used to examine the systematic evaluation of the impact of feature selection based on Pearson's correlation on the performance of the linear regression model. The results revealed that maximum fresh and dry biomass of mustard was observed by 26.38 and 38.18 % with hydrochar 1 %, whereas lemon biochar at 2 % reduced fresh and dry biomass up to 34.0 and 53.0 % than control. The immobilization of Cd and Pb was observed by 83.70 and 71.15 % with thiourea-vegetable modified biochar at 2 %, As 71.62 % with hydrochar 2 %, Ni 80.84 % with thiourea-vegetable modified biochar 2 %, Cu 66.32 % with and Zn 36.30 % with thiourea-vegetable modified biochar at 2 % than control. However, the maximum mobilization of Cu in soil was observed by 30.3 % with lemon biochar 2 %, similarly for Zn 37.36 % with hydrochar 2 % as compared with other treatments. The phyto-availability of Cd, Pb, As and Cu in the mustard shoot and root biomass was reduced except Ni and Zn in soil than control. It was observed that using the machine learning regression analysis approach, variability in treatments effectiveness is evident across different feature correlation thresholds. This study clearly shows that the beneficial role of studied amendments on mustard growth and reduced bioavailability of heavy metal(loid)s and enhance primary macronutrients in alkaline polluted soil. It is suggested that future studies may be conducted on combined application of studies amendments on plant growth, immobilization of heavy metal(loid)s in multi-metal polluted soil under different field conditions.

In-situ stabilization of potentially toxic elements in two industrial polluted soils ameliorated with rock phosphate-modified biochars.

The present study was aimed at determining the efficacy of rock phosphate (RP) 3% loaded in a green coconut shell, chicken manure, and vegetable waste to make green coconut-modified biochar (GMB), chicken manure modified-biochar (CMB), and vegetable waste-modified biochar (VMB) in the fixation of Cr, Pb, Cu, Zn, Ni, and Cd in Sharafi goth and Malir polluted soils. The impact of RP impregnated with organic waste material to produce modified biochars (MBs) on stabilizing PTEs from polluted soils and reducing their uptake by mustard plant has not yet been thoroughly investigated. All modified BCs in 0.5, 1, and 2% doses were used to stabilize Cr, Pb, Cu, Zn, Ni, and Cd in two polluted soils and to reduce their uptake by the mustard plant. The obtained results revealed that the maximum mustard fresh biomass was 17.8% higher with GMB 1% in Sharafi goth polluted soil and 25% higher with VMB 0.5% in Malir polluted soil than in the control treatment. After applying modified BCs, immobilization of Cr, Pb, Cu, Ni, and Cd was observed in both soils and it reduced the uptake of these elements by mustard plants. On the other hand, although Zn mobilization increased by 0.38% for CMB 0.5% and by 5.9% for VMB 0.5% in Sharafi goth polluted soil, as well as by 3.15% for GMB 1%, 6.34% for GMB 2%, and 4.78% for VMB 0.5% in Malir polluted soil, this was due to changes in soil pH and OM. It was found that GMB 1%, CMB 0.5%, and VMB 0.5% have the potential to increase Zn uptake by mustard, while VMB 2% can reduce the element uptake by the plant. Redundancy analysis showed that soil chemical parameters were negatively correlated with PTEs in both soils and reduced their uptake by mustard. The present study revealed that MBs can stabilize PTEs in industrial and wastewater soils polluted with multiple metals and reduce their uptake by plants.

Lanthanum hydroxide engineered sewage sludge biochar for efficient phosphate elimination: Mechanism interpretation using physical modelling.

In the present study, lanthanum hydroxide (La OH)-engineered sewage sludge biochar (La-SSBC) was utilized for efficient phosphate elimination from an aqueous medium. A high adsorption capacity of 312.55 mg P/g was achieved using La-SSBC at 20 °C, which was an excellent adsorbent performance in comparison to other biochar-based adsorbents. Additionally, the performance of La-SSBC was stable even at wider range of pH level, the existence of abundant active anions, and recycling experiments. Statistical physics modeling with the fitting method based on the Levenberg-Marquardt iterating algorithm, as well as various chemical characterizations, suggested the unique double-layered mechanism of phosphate capturing: one functional group of La-SSBC adsorbent describing a prone direction of the PO4 ions on the stabilize surface in a multi-ionic process, forming the first layer adsorption. Additionally, SSBC played an important role by releasing positively charged cations in solution, overcoming the electronic repulsion to form a second layer, and achieving excellent adsorption capacity. The calculation of multiple physicochemical parameters including adsorption energy further evidenced the process. This two-layered mechanism sheds light on the complex interaction between phosphate and biochar. Moreover, the management of sewage sludge associated with the requirement of cost-effectively and environmentally acceptable mode. Therefore, the present investigation demonstrated an efficient approach of the simultaneous sewage sludge utilization and phosphate removal.

Screening of Chinese mustard (Brassica juncea L.) cultivars for the phytoremediation of Cd and Zn based on the plant physiological mechanisms.

Brassica juncea L. is an attractive species in PTMs contaminated soil remediation ascribing to its high tolerance under stress and great accumulation capacity of metals. To identify the potential Cd/Zn accumulators from numerous different Chinese mustard cultivars for practical phytoremediation is a promising strategy in China. In present work, a pot experiment involving elevated Cd/Zn concentrations was performed among 21 cultivars. Regarding physiological and biochemical indicators under Cd/Zn stress, principal component analysis and cluster analysis were used for cultivar tolerance evaluation and classification. Results showed that BJ (Bao Jie, var. involutus) cultivar was distinguished as a potential phytoremediation candidate comparing with other cultivars. Moreover, BJ accumulated the maximum Cd content of 63.85 and 77.29 mg kg-1 DW in shoots and roots, respectively, and the maximum Zn uptake by BJ were 6693 and 4777 mg kg-1 DW in shoots and roots, respectively. Accordingly, BJ had the highest Cd/Zn tolerance, remarkable accumulation and translocation capacity (accumulation factor (AF) > 1 for Cd and Zn; translocation factor (TF) > 0.8 for Cd and TF > 1 for Zn). In addition, the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of the mustard increased initially under low Cd/Zn stress as compared to the control and then declined dramatically with the increasing metals exposure concentration. Therefore, the antioxidant enzymes may play a protective role against reactive oxygen species (ROS) under low Cd/Zn stress, whereas the defense system might be collapsed under relatively high Cd/Zn stress. Furthermore, the enhanced Cd/Zn exposure led to an increase in malondialdehyde (MDA) content in the mustard cultivars, indicating that Cd/Zn had induced more severe oxidative stress and higher degree of lipid peroxidation had occurred. The present investigation results indicated that BJ (Bao Jie, var. involutus), as a native cultivar, can be further applied in the field trials of phytoremediation practices in contaminated soil.

Phytostabilization of Pb-Zn Mine Tailings with Amorpha fruticosa Aided by Organic Amendments and Triple Superphosphate.

A greenhouse pot trial was conducted to investigate the effect of organic amendments combined with triple superphosphate on the bioavailability of heavy metals (HMs), Amorpha fruticosa growth and metal uptake from Pb-Zn mine tailings. Cattle manure compost (CMC), spent mushroom compost (SMC) and agricultural field soil (AFS) were applied to tailings at 5%, 10%, 20% and 30% w/w ratio, whereas sewage sludge (SS) and wood biochar (WB) were mixed at 2.5%, 5%, 10% and 20% w/w ratio. Triple superphosphate (TSP) was added to all the treatments at 4:1 (molar ratio). Amendments efficiently decreased DTPA-extracted Pb, Zn, Cd and Cu in treatments. Chlorophyll contents and shoot and root dry biomass significantly (p< 0.05) increased in the treatments of CMC (except T4 for chlorophyll b) and SMC, whereas treatments of SS (except T1 for chlorophyll a and b), WB and AFS (except T4 for chlorophyll a and b) did not show positive effects as compared to CK1. Bioconcentration factor (BCF) and translocation factor (TF) values in plant tissues were below 1 for most treatments. In amended treatments, soluble protein content increased, phenylalanine ammonialyase (PAL) and polyphenol oxidase (PPO) decreased, and catalase (CAT) activity showed varied results as compared to CK1 and CK2. Results suggested that A. fruticosa can be a potential metal phytostabilizer and use of CMC or SMC in combination with TSP are more effective than other combinations for the in situ stabilization of Pb-Zn mine tailings.

Direct and residual impacts of zeolite on the remediation of harmful elements in multiple contaminated soils using cabbage in rotation with corn.

In the present work, in-situ two pot trials were conducted to explore the direct and residual influences of zeolite (ZL) on plant height, dry biomass and bioavailability of Pb, Cd, Cu, and Zn by growing cabbage followed by corn in goldmine-contaminated (GM-C), smelter factory-contaminated (SF-C), and farmland-contaminated (FL-C) soils. Initially, a single treatment of ZL was applied at 20 t/ha, and cabbage was grown under greenhouse pot conditions. After cabbage harvesting, corn was grown in the same pots without additional application of ZL. The results indicated that ZL as an amendment evidently promoted the cabbage and corn yields, whereas the residual influence of ZL did not promote corn dry matter yield in SF-C and FL-C soils compared to CK. Incorporation of ZL potentially decreased the mobility of Pb, Cd, Cu and Zn in contaminated soils after harvesting cabbage and corn compared with CK. In both crops, the Pb, Cd, Cu and Zn contents in plants root and shoot biomasses were dramatically reduced by the direct and residual impacts of ZL rather than CK. This study highlights that the direct and residual influences of ZL at a 20 t/ha application rate have the possibility to support the reclamation of soils polluted with harmful elements and that, by itself, ZL can promote plant growth and increase the value of field crops. The detailed studied regarding residual influence of ZL for restoration of multi-metal polluted soils would be confirmed at the ex-situ condition.

Comparison of Cd2+ adsorption onto amphoteric, amphoteric-cationic and amphoteric-anionic modified magnetic bentonites.

Organic-magnetic bentonites (OMBts), i.e., amphoteric modified MBt (BS-MBt), amphoteric-cationic modified MBt (BS-CT-MBt) and amphoteric-anionic modified MBt (BS-SDS-MBt), obtained by modifying magnetic bentonite (MBt) with amphoteric surfactant (BS), cationic surfactant (CT) and anionic surfactant (SDS) were investigated with the aim to remove cadmium (Cd2+). The modifier contents, surface charge and Cd2+ adsorption performances of OMBts were compared, and the influences of pH, temperature and ionic strength on Cd2+ removal were evaluated. Results showed that modifier contents of OMBts increased in the order: BS-CT-MBt > BS-MBt > BS-SDS-MBt. Although CEC of adsorbents increased in the order: MBt > BS-MBt > BS-SDS-MBt > BS-CT-MBt. The BS-MBt exhibited the highest Cd2+ adsorption capacity (233.19 mmol kg-1) than other adsorbents. The adsorption isotherms could be well described by Langmuir model. The Cd2+ adsorption capacities on MBt and OMBts increased with an increase in pH, temperature and with a decrease of ionic strength. According to characterizations (FT-IR and XPS) and experiments, Cd2+ adsorption on MBt and OMBts most possibly involved electrostatic interaction, ion exchange, and surface complexation. Furthermore, the adsorption of Cd2+ on BS-MBt was also attributed to the chelation. The amidocyanogen group of BS-CT-MBt inhibited adsorption of Cd2+ due to electrostatic repulsion, while Cd2+ was adsorbed on BS-SDS-MBt through electrostatic attraction induced by the sulfo group.

Residual effects of tobacco biochar along with different fixing agents on stabilization of trace elements in multi-metal contaminated soils.

The residual effect of tobacco biochar (TB ≥ 500°C) mono and co-application with Ca-hydroxide (CH), Ca-bentonite (CB) and natural zeolite (NZ) on the bio-availability of trace elements TE(s) in alkaline soils has not been deeply studied yet. A pot study that had earlier been investigated TB mono and blended with CH, CB and NZ on the immobilization of Pb, Cu Cd, and Zn by Chinese cabbage. Maize crop in the rotation was selected as test plant to assess the residual impact of amendments on stabilization of Pb, Cu Cd, and Zn in mine polluted (M-P), smelter heavily and low polluted (S-HP and S-LP, respectively) soils. The obtained results showed that stabilization of Pb, Cd, Cu and Zn reached 63.84% with TB + CB, 61.19% with TB + CH, 83.31% with TB + CH and 35.27% with TB + CH for M-P soil, 36.46% with TB + NZ, 38.46% with TB + NZ, 19.40% with TB + CH and 62.43% with TB + CH for S-LP soil, 52.94% TB + NZ, 57.65% with TB + NZ, 52.94% with TB + NZ, and 28.44% with TB + CH for S-LP soil. Conversely, TB + CH and TB alone had mobilized Pb and Zn up to 19.29% and 34.96% in M-P soil. The mobility of Zn reached 8.38% with TB + CB and 66.03% with TB for S-HP and S-LP soils. The uptake and accumulation of Pb, Cd, Cu and Zn in shoot and root were reduced in three polluted soils. Overall, the combination of TB along with CH, CB and NZ has been proven to be effective in Pb, Cd, Cu and Zn polluted mine/smelter soils restoration.

Evaluation of orange peel waste and its biochar on greenhouse gas emissions and soil biochemical properties within a loess soil.

The environmentally safe disposal of the large quantity of orange peels waste produced each day causes economic and environmental problems, which after conversion into biochar via pyrolysis technique might be used as an effective soil amendment. In this study, a 90-day incubation experiment was conducted to investigate the effects of orange peel waste and waste-derived biochar amendments on greenhouse gas emissions (GHG), soil biochemical properties, and soil enzyme activities. There were five treatments with different amendment levels: control without an amendment (Control), orange waste 1% (W1), orange waste 2% (W2), orange waste biochar 1% (B1), and orange waste biochar 2% (B2). The results showed that, compared with control, the amendments decreased cumulative N2O emissions by 59.2% (B2), 45.2% (B1), 20.6% (W2) and 10.2% (W1), respectively; and increased cumulative CH4 emissions by 81.7% (W1), 84.4% (W2), 75.8% (B1) and 74.9% (B2), respectively. Cumulative CO2 emissions decreased for the B1 (29.3%) and B2 (43.5%) over the waste treatments. While soil pH, SOC, nitrate nitrogen (NO3--N) and enzyme activities (urease and catalase) were significantly increased with the passage of time from the biochar amendments, ammonium nitrogen (NH4+-N) and invertase activities did not show this trend with time. Our study suggests that orange peel waste conversion to biochar should be a viable alternate method of disposal since land application resulted in reduced GHG and improvements in soil fertility.

Mono-and co-applications of Ca-bentonite with zeolite, Ca-hydroxide, and tobacco biochar affect phytoavailability and uptake of copper and lead in a gold mine-polluted soil.

We assessed the efficacy of Ca-bentonite (CB) alone and combined with Ca-hydroxide (CH), tobacco biochar (TB), and zeolite (ZL) aiming to immobilize Cu and Pb and decrease their bioavailability and uptake by pak choi followed by maize in a mining contaminated soil. The CB alone was able to decrease the availability and uptake of Cu and Pb by pak choi and maize. The mono- and multi-combination of CH, TB, and ZL with CB showed contradictory impact on the availability and uptake of Cu and Pb as compared to the mono-application of CB. The combination of CB with ZL and CH + ZL reduced the uptake of Pb by pak choi and maize, while the combination of CB with TB and ZL reduced the uptake of Cu by pak choi and maize as compared to the mono-application of CB. The co-application of CB with CH increased the phytoextraction of Cu by maize and Pb by pak choi shoots as compared to the mono-application of CB. We conclude that modified clays such as CB alone or combined with ZL, TB, and/or CH might be suitable candidates for phytomanagement of Cu and Pb contaminated soils.

EDTA and organic acids assisted phytoextraction of Cd and Zn from a smelter contaminated soil by potherb mustard (Brassica juncea, Coss) and evaluation of its bioindicators.

Phytoremediation of contaminated soil is an in-situ reclamation technique for removal of potentially toxic metals through hyperaccumulator plants. Potherb mustard (Brassica juncea, Coss.) is less explored for its assisted phytoextraction potential to restore and accelerate potentially toxic metals removal from smelter-contaminated soil. In this study, different levels of ethylene diamine tetraacetic acid (EDTA) alone and combined with citric acid (CA) and oxalic acid (OA) were applied in a greenhouse pot experiment. Chelates added on 25th d and 25/35th d after sowing, enhanced cadmium (Cd) and zinc (Zn) bioavailability in soil due to complexation. As a result, Cd and Zn in shoot and root were significantly amplified by 1.7, 2.15 and 1.93, 2.7 folds than control, respectively. Shoot and root dry weight significantly reduced and ranged between 4.13-9.91 and 0.21-0.77 g pot-1, respectively. The toxicity induced by potentially toxic metals in plant imposed a series of biological responses. Plant antioxidants like Phenylalanine ammomialyase (PAL), polyphenol oxidase (PPO) Catalase (CAT) content increased, except the peroxidase (POD) with the addition of chelating agents. Besides, biological concentration factor (BCF) of Cd and Zn, translocation factor (TF) of Cd were notably elevated (>1.0), while TF of Zn was reduced. Pearson correlation analysis showed a positive relation between DTPA-extractable and shoot concentration of Cd and Zn, whereas it showed negative correlation with plant dry weight. In general, chelate-assisted phytoremediation of smelter contaminated soil proved effective in this study, and followed the order: EDTA > EDTA + CA ≈ EDTA + OA > CK.

Screening of native plants from wasteland surrounding a Zn smelter in Feng County China, for phytoremediation.

Phytoremediation is regarded as one of the most cost-effective and environmentally friendly strategies for potentially toxical metals (PTMs) contaminated soil remediation. Despite that, continuous studies are conducting to explore the potential plant species in order to achieve enhanced remediation efficiencies. Therefore, in this study, a field investigation was conducted to screen the potential phytoremediation plants from a contaminated site in the surrounding area of a Zn smelter in Feng Country, China. Results indicated that soils in the studied area were severely contaminated with Cd and Zn, while the contents of other metals (Cu, Pb, and Ni) were below the allowanced threshold. Moreover, the contamination was more serious in areas closer to the smelter. The elevated level of contamination had great impacts on plant diversity and abundance. Fifty-nine plant species belonging to 28 families were identified in the studied area, of which plants from the Asteraceae family and herbs were most frequently observed. Plants demonstrated differentiated potential on metal accumulation and translocation, and the total Cd, Cu, Pb, and Zn contents in the aerial parts of plants ranged from 5.57 to 268.5, 14.34 to 140.90, 10.43 to 570.3, and 110.3 to 1350 mg kg-1, respectively. Symphytum officinale Linn. distinguished itself from the various plants as a promising plant candidate for soil remediation, due to its great capacities for absorbing Cd, Pb, and Zn. Specifically, an individual Symphytum officinale Linn. plant can accumulate up to 5.54, 21.0, and 52.9 mg Cd, Pb, and Zn in its aboveground parts (20.67 g dry weight). Results from this study can provide a reference for the phytoremediation of PTMs contaminated soil in this area or other places with similar soil and climate conditions.

Nitrate removal by combined heterotrophic and autotrophic denitrification processes: Impact of coexistent ions.

In this current study, sawdust and zero-valent iron (Fe0) were used as co-electron donors to evaluate the effects of coexistent ions on the combined heterotrophic and autotrophic denitrification (HAD) processes. The results showed that HCO3- and SO42- drastically enhanced nitrate removal. The promotion effect derived from both biological and chemical process by HCO3- and chemical process by SO42-. However, Ca2+ ions would remarkably increase nitrate removal due to promoting the electron transfer and the metabolic activities of bacteria, whereas the Cu2+ ions inhibited the biological process due to the deleterious effect on bacteria. Meanwhile, Fe2+ and Fe3+ ions exhibited inhibition effect firstly because of their toxicity to bacteria and promotion subsequently due to their enhancement on Fe0 chemical denitrification. Moreover, byproducts such as nitrite, ammonium, dissolved organic carbon (DOC), etc. were also influenced by common ions.

Influence of biochar on volatile fatty acids accumulation and microbial community succession during biosolids composting.

The impact of biochar amendment on volatile fatty acids (VFAs) and odor generation during the biosolids-wheat straw composting was investigated. Five treatments were design using the same mixture of biosolids-wheat straw with different dosage of biochar blending (2%, 4%, 8% and 12% on dry weight basis) and without biochar applied treatment served as control. The results of VFAs and Odour Index (OI) profile designated that compost with 8-12% biochar became more rapidly humified with less quantity of VFAs and OI generation content compared to control. Consequently, the VFAs degrading and total bacterial abundance are also significantly higher recorded in 8-12% biochar than 2% biochar and control. In addition, 8-12% biochar applied treatment has significantly maximum close correlation among the all physicochemical and gaseous emission parameters. Finally, results designated that higher dosage of biochar (8-12% biochar) was more feasible approach for biosolids composting.

Beneficial effects of tobacco biochar combined with mineral additives on (im)mobilization and (bio)availability of Pb, Cd, Cu and Zn from Pb/Zn smelter contaminated soils.

The efficacy of tobacco biochar (TB) alone and in combined with mineral additives: Ca-hydroxide (CH), Ca-bentonite (CB) and natural zeolite (NZ), on immobilization of Pb, Cd, Cu and Zn, via reduce its (bio) availability to plants were investigated. The soils were collected from Tongguan contaminated (TG-C), Fengxian heavily contaminated (FX-HC) and Fengxian lightly contaminated (FX-LC) fields, Shaanxi province, China. The contaminated top soils were treated with low-cost amendments with an application rate of 1% and cultivated by Chinese cabbage (Brassica campestris L.) under greenhouse condition. Results showed that the all amendments (p < 0.05) potentially maximum reduced the DTPA-extractable Pb 82.53, Cd 31.52 and Cu 75.0% with TB + NZ in FX-LC soil, while in case of Zn 62.21% with TB + CH in FX-HC soil than control. The addition of amendments clearly increased dry biomass of Brassica campestris L. as compared with un-amended treatment (except TB + CH). Furthermore, these amendments markedly increased the uptake by plant shoot viz, Cd 10.51% with TB alone and 11.51% with TB + CB in FX-HC soil, similarly in FX-LC Cd increased 5.15% with TB + CH and 22.19% with TB + NZ, respectively. In same trend the Cu uptake in plant shoot was 19.30% with TB + CH in TG-C, whereas 43.90 TB + CH and 19.24% with TB + NZ in FX-LC soil. On the other hand as compared to control Cu accumulation in plant root was observed by TB, TB + CH and TB + CB treatments, while maximum uptake was 62.41% with TB + CH in TG-C soil. Consequently, except TB + CH treatment the chlorophyll content potentially increased in all amendment than control treatment, because of changes in soil EC, pH but increased CEC values after application of amendments. The results of this pot experiment are promising but they will further need to be confirmed with long-term field experiments.

Impact of CaO, fly ash, sulfur and Na2S on the (im)mobilization and phytoavailability of Cd, Cu and Pb in contaminated soil.

Soil heavy metals pollution is a serious problem worldwide due to its potential human health risks through food chain. Therefore, a sustainable solution is needed to efficiently remediate HMs contaminated soils. Our study aimed to assess the impact of CaO, fly ash, sulfur, and Na2S on the immobilization of Cd, Cu, and Pb and their uptake by Chinese cabbage (Brassica rapa chinensis) in a contaminated soil. The concentration of DTPA-extractable Cd, Cu, and Pb was significantly decreased as compared to control in treated soil. However, the solubility of Cd, Cu, and Pb has increased at greater extent in soil system which favored the uptake of metals in roots and shoots of Chinese cabbage. In general, Cd uptake was significantly increased in shoots followed by roots as compared to control. In addition, Cu has also same trend of increased uptake in shoots as compared to roots. However, the uptake Pb in shoots was considerably increased in Na2S treated samples whereas roots have shown great potential for Pb uptake in CaO treated samples as compared to control. Although, sulfur treatments had efficiently immobilized metals but reduced soil pH to highly acidic level which restricted the growth of Chinese cabbage in sulfur treated samples. We assume that sulfur amendment could be applied for immobilization of metals in alkaline soils rather than acidic soils to achieve better immobilization results. In order to achieve sustainable phytoextraction of Cd, Cu, and Pb using CaO, FA, and Na2S, the non-edible hyperaccumulators species are suggested to be investigated in future studies.

Role of biochar amendment in mitigation of nitrogen loss and greenhouse gas emission during sewage sludge composting.

The objective of the present study was to mitigate the greenhouse gas (GHG) emissions during composting of dewatered fresh sewage sludge (DFSS) employing biochar combined with zeolite (B+Z) and low dosage of lime (B+L). The 12% biochar was mixed at a 10%, 15% and 30% of zeolite and 1% lime, while without any additives was used as control. The results indicated that the combine use of B+Z was significantly increased the enzymatic activities and reduced the ammonia loss 58.03-65.17% as compare to B+L amended treatment, while CH4 92.85-95.34% and N2O 95.14-97.28% decreased than control. The B+L1% amendment significantly increased the organic matter degradation but the reduction was lower than B+Z and that could reduce the CH4 and N2O emission by 55.17-63.08% and 62.24-65.53% as compare to control, respectively. Overall our results demonstrated that 12%B+Z10% addition into DFSS can be potentially used to improve the DFSS composting by mitigation of GHG emission and nitrogen loss.

Influence of zeolite and lime as additives on greenhouse gas emissions and maturity evolution during sewage sludge composting.

This study aimed to evaluate the role of different amount of zeolite with low dosage of lime amendment on the greenhouse gas (GHGs) emission and maturity during the dewatered fresh sewage sludge (DFSS) composting. The evolution of CO2, CH4, NH3 and N2O and maturity indexes were monitored in five composting mixtures prepared from DFSS mixed with wheat straw, while 10%, 15% and 30% zeolite+1% lime were supplemented (dry weight basis of DFSS) into the composting mass and compared with treatment only 1% lime amended and control without any amendment. The results showed that addition of higher dosage of zeolite+1% lime drastically reduce the GHGs emissions and NH3 loss. Comparison of GHGs emissions and compost quality showed that zeolite amended treatments were superior than control and 1% lime amended treatments. Therefore, DFSS composting with 30% zeolite+1% lime as consortium of additives were found to emit very less amount of GHGs and gave the highest maturity than other treatments.

Enhancing phosphate adsorption by Mg/Al layered double hydroxide functionalized biochar with different Mg/Al ratios.

Mg/Al ratio plays a significant role for anion adsorption by Mg/Al-layered double hydroxides (Mg/Al-LDHs) modified biochar. In this study, Mg/Al-LDHs biochar with different Mg/Al ratios (2, 3, 4) were prepared by co-precipitation for phosphate removal from aqueous solution. Factors on phosphate adsorption including Mg/Al ratio, pH, and the presence of other inorganic anions were investigated through batch experiments. Increasing Mg/Al ratio in the Mg/Al-LDHs biochar composites generally enhanced phosphate adsorption with Langmuir adsorption maximum calculated at 81.83mg phosphorous (P) per gram of 4:1Mg/Al-LDHs biochar at pH3.0. The adsorption process was best described by the pseudo-second-order kinetic model. Solution pH had greater effects on the phosphate adsorption by Mg/Al LDHs biochar composites with lower Mg/Al ratios. The presence of other inorganic anions decreased the phosphate adsorption efficiency in the order of F(-) > SO4(2-) > NO2(-) >Cl(-). Phosphate adsorption mechanism involves ion exchange, electrostatic attraction and surface inner-sphere complex formation. Overall, Mg/Al-LDHs biochar composites offer a potential alternative of carbon-based adsorbent for phosphate removal from aqueous solution.

Recovery of phosphate from aqueous solution by magnesium oxide decorated magnetic biochar and its potential as phosphate-based fertilizer substitute.

The present study deals with the preparation of a novel MgO-impregnated magnetic biochar (MMSB) for phosphate recovery from aqueous solution. The MMSB was evaluated against sugarcane harvest residue biochar (SB) and magnetic biochar without Mg (MSB). The results showed that increasing Mg content in MMSB greatly improved the phosphate adsorption compared to SB and MSB, with 20% Mg-impregnated MMSB (20MMSB) recovering more than 99.5% phosphate from aqueous solution. Phosphate adsorption capacity of 20MMSB was 121.25mgP/g at pH 4 and only 37.53% of recovered phosphate was desorbed by 0.01mol/L HCl solutions. XRD and FTIR analysis showed that phosphate sorption mechanisms involved predominately with surface electrostatic attraction and precipitation with impregnated MgO and surface inner-sphere complexation with Fe oxide. The 20MMSB exhibited both maximum phosphate sorption and strong magnetic separation ability. Overall, phosphate-loaded 20MMSB significantly enhanced plant growth and could be used as a potential substitute for phosphate-based fertilizer.