Comparative short-term effects of sewage sludge and its biochar on soil properties, maize growth and uptake of nutrients on a tropical clay soil in Zimbabwe

Soil application of biochar from sewage could potentially enhance carbon sequestration and close urban nutrient balances. In sub-Saharan Africa, comparative studies investigating plant growth effect and nutrients uptake on tropical soils amended with sewage sludge and its biochar are very limited. A pot experiment was conducted to investigate the effects of sewage sludge and its biochar on soil chemical properties, maize nutrient and heavy metal uptake, growth and biomass partitioning on a tropical clayey soil. The study compared three organic amendments; sewage sludge （SS）, sludge biochar （SB） and their combination （SS＋SB） to the unamended control and inorganic fertilizers. Organic amendments were applied at a rate of 15 t ha-1 for SS and SB, and 7.5 t ha-1 each for SS and SB. Maize growth, biomass production and nutrient uptake were significantly improved in biochar and sewage sludge amendments compared to the unamended control. Comparable results were observed with F, SS and SS＋SB on maize growth at 49 d of sowing. Maize growth for SB, SS, SS＋SB and F increased by 42, 53, 47, and 49%, respectively compared to the unamended control. Total biomass for SB, SS, SS＋SB, and F increased by 270,428, 329, and 429%, respectively compared with the unamended control. Biochar amendments reduced Pb, Cu and Zn uptakes by about 22% compared with sludge alone treatment in maize plants. However, there is need for future research based on the current pot experiment to determine whether the same results can be produced under field conditions.

β-FeOOH Modified Sludge Biochar as Efficient Adsorbent for Phosphate Removal

β⁃FeOOH modified sludge biochar(FSBC)was prepared and investigated in this work to remove phosphate from water via adsorption.FSBC exhibited superior adsorption performance for phosphate with the maximum adsorption amount of 27.17 mg/g at 25℃.The specific adsorption capacity of FSBC was 57.8%higher than that of commercial activated carbon at pH 5 with the initial phosphate concentration of 10 mg/L.Coexisting anions can inhibit the adsorption of phosphate,but cations(Cr(VI)and Cd^(2+))exhibited some promotion effect.The results of kinetic and isotherm models and characterization analysis in combination indicated chemical adsorption,as electrostatic interaction,metal phosphate precipitation and hydrogen bonding may be the dominant process.The adsorption of phosphate onto FSBC was a monolayer adsorption,and the process was endothermic.After four adsorption/desorption cycles,the adsorption capacity of FSBC for phosphate decreased by 36.4%,which was in a distinct comparison with the 57.5%of SBC.

Stability of potentially toxic elements in municipal sludge biochars modified by MgCl2 and phosphate

Municipal wastewater sludge can be pyrolyzed as biochars to better use nutrients and stabilize carbon compared with other typical technologies,such as landfill and incineration.However,sludge-derived biochars might contain large amounts of potentially toxic elements(PTEs),such as Zn,Cu,Cr,Ni,Pb,and As.The stability of PTEs in biochars might be improved by higher pyrolytic temperatures,which can be further improved by different modifications.Herein,PO4-modification at 300°C and Cl-modification at 700°C were carried out,respectively,to enhance the stability of PTEs.Various leaching tests have been performed to assess the stability of PTEs in biochars,including the synthetic precipitation leaching procedure(SPLP),toxicity characteristic leaching procedure(TCLP),diethylenetriamine pentaacetate(DTPA)extraction,and in vitro simple bioaccessibility extraction test(SBET).The morphological structure,elemental mapping,and mineral formation of the pristine and modified biochars were studied by scanning electron microscopy–energy-dispersive X-ray spectroscopy(SEM–EDS)and X-ray diffraction(XRD).Our results suggested that the leachability,mobility,plant-availability,and bioaccessibility of most PTEs were decreased by pyrolysis,yet the total contents of PTEs were elevated,especially at 700°C.Generally,modification by phosphates and MgCl2 enhanced the stability of PTEs in biochars.Nevertheless,it should be noted that higher bioaccessibility of PTEs was observed in biochars of P-modification than Cl-modification,which is associated with the dissolution of phosphate precipitates under acidic conditions(pH<2).Additionally,Cl-modification leads to higher plant-available Zn and Cu and bioaccessible Zn compared with the unmodified biochar produced at 700°C.

Moderate sewage sludge biochar application on alkaline soil for corn growth:a field study

In view of the risks induced by the inhibitory effects of applying impracticably large amounts of sewage sludge biochar(SSB)to the alkaline soil,this field study investigated the influence of moderate biochar amendments(0,1500,4500,and 9000 kg/hm2)on corn growth,alkaline soil properties,and the uptake of potentially toxic elements(PTEs).The results showed that applying more SSB would decrease the ammonium nitrogen concentration and increase the available phosphorus and potassium concentrations,which inhibited corn plant growth because of high background nutrient levels of the alkaline soil.When the alkaline soil was amended with 1500 kg/hm2 SSB,the dry weight of 100 niblets increased from 32.11 g in the control to 35.07 g.There was no significant variation in the total concentration of PTEs in the soil.The concentrations of Mn,Ni,Cu,and Zn in niblets decreased from 5.54,0.83,2.26,and 27.15 mg/kg in the control to 4.47,0.62,1.30,and 23.45 mg/kg,respectively.Accordingly,the health risk from corn consumption was significantly reduced.Furthermore,the combination of SSB and fertilizer improved corn growth and reduced the risk of consumption of PTEs.Therefore,considering the increase in corn fruit yield and the decrease in consumption risk,applying 1500 kg/hm2 of biochar to alkaline soils is a realistically achievable rate,which can broaden the utilization of SSB for remediation of different types of soil.

Comparative assessment for removal of anionic dye from water by different waste-derived biochar vis a vis reusability of generated sludge

In this study,four biochars prepared from different crop residue waste i.e.sugarcane bagasse(SBB),coconut shell(CNB),paddy straw(PDB),and distilled waste of lemongrass(LGB)were evaluated for removal of Remazol Brilliant Blue R from the aqueous system.The RBBR adsorption capacities of biochar were 97-79%for SBB,99.9-99.47%for CNB,66.1-48%for PDB,and 78-68%for LGB,dominantly controlled by their aromaticity and mineral content.The Langmuir and Freundlich isotherms and pseudo-second-order kinetic models have described the chemisorption of RBBR on biochar surfaces.The thermodynamic data suggested that adsorption was spontaneous and endothermic.These biochars demonstrated excellent reusability(till four cycles with 50-61%regeneration).The purified water and biochar dye sludge demonstrated no phytotoxicity.The findings obtained in this study may provide supports for the potential of biochars for anionic dye removal from water and utilization of generated sludge for zero waste-producing technologies in the future.