A study on carbon storage in soil using biosolids

Wijesekara, Hasintha

Title: A study on carbon storage in soil using biosolids
Creator: Wijesekara, Hasintha
Relation: University of Newcastle Research Higher Degree Thesis
Resource Type: thesis
Date: 2018
Description: Research Doctorate - Doctor of Philosophy (PhD)
Description: Land application of biowastes including biosolids has been identified as one of the management strategies in soil organic carbon (SOC) sequestration, thereby contributing to potential “direct action” approaches to mitigating climate change. This study aimed to understand the effects of biosolids application on C storage in soils. The specific objectives were to: (i) demonstrate the driving factors and their magnitudes on SOC storage in biosolids amended soils; (ii) examine the effect of co-composting as a feasible strategy to stabilize C in biosolids; (iii) study the effect of biosolid-derived inorganic C (i.e., particulate plastics) on C dynamics and modulation of contaminants in soil, and (iv) to monitor CO2 fluxes and SOC dynamics in biosolids amended soil under field conditions. Firstly, a meta-analysis was conducted to compare quantitatively SOC changes from data derived from 297 field studies over seven variables: soil depth, soil texture, clay content, type of biosolids, application type, time after application (i.e., age) and cumulative biosolids C input rate. A statistical model (i.e., meta-analytic multivariate) was developed to understand the drivers for SOC stock changes resulting from biosolids application. Among the seven variables, the cumulative biosolids C input rate, age, soil depth and type of biosolids were identified as the main drivers of SOC stock change in soil. The highest mean difference for SOC% of 4.7 [3.1–6.4], 95% confidence interval (CI) was observed at 0–15 cm soil depth for a cumulative biosolids C input of 100 Mg ha^-1 at one year after biosolids application. Although years after biosolids application demonstrated a negative relationship with SOC stocks, mineralization of C in biosolids-applied soils is slow, as indicated with the SOC% decrease from 5.0 to 4.4 at 0–15 cm soil depth over five years of 100 Mg ha^-1 biosolids C input. Soil depth illustrated a strong negative effect with SOC stocks decreasing by 1.3% at 0–15 cm soil depth at a cumulative biosolids C input of 100 Mg ha^-1 over a year. Overall, the model estimated an effect of 2.8 SOC% change, indicating that application of biosolids increases SOC stocks and therefore has the potential to be a strategy for soil C sequestration. Secondly, to examine the effect of biosolid-stabilizing materials on C mineralization, biosolids were co-composted with various nanoclay and alkaline materials. Fluidized bed boiler ash (FBA), flue-gas desulphurization gypsum (FGD), red mud (RM), and garden lime were used as the C stabilizing materials. In the co-composting process, biosolids or poultry manure (i.e., biowastes) were mixed with the stabilizing materials at the rate of 10% (w/w) and incubated in an aerobic digester for six months. The stability of C in co-composts was examined by monitoring the decomposition of co-composted biowastes in an arable soil by measuring the release of CO₂, dissolved organic C (DOC) and chemical fractionation of C. The DOC concentrations of final co-composted products were less (~ 20%) in the presence than absence of the amendments, indicating the enhanced stabilization of C in composts in the presence of amendments. In the presence of the stabilizing materials, there was an increase in the non-labile and residual C fractions in the co-composted products. The energy dispersive X-ray (EDX) data for co-composts provided evidence for the association of Ca, Fe and Al with SOC, thereby contributing to the stabilization of C in co-composts. The co-composting of biowaste with the stabilizing materials resulted in ~ 54% decrease in decomposition when applied to soil. There was no significant difference in microbial biomass C (MBC) in soil between the stabilized composts and unamended composts, indicating the C stabilizing materials were unlikely to affect the microbial growth in soil. Stabilized composts increased the priming effect (PE) values in soil, indicating that co-composts enhanced the potential mineralization of SOC. Co-composted biosolids with garden lime and RM were found to be most effective for SOC storage due to their low PE on SOC. Thirdly, a laboratory incubation study examined the effect of biosolid-derived inorganic C (i.e., particulate plastics) on C dynamics and modulation of the toxicity of organic and inorganic contaminants in soil. Particulate plastics (i.e., microplastics) are an inorganic C input to soils resulting from biosolid application. Particulate plastics are also likely to interact with biosolid-derived organic and inorganic contaminants, thereby influencing the microbial functions in soil. Two types of particulate plastics, pristine polyethylene (PPP) and surface modified (BSPP) plastics were used to monitor their impact on microbial activity and C storage in soil. Sandy soil samples were mixed with the two types of particulate plastics at the rate of 6.4% (w/w) in soil. Perfluorooctane sulfonate (PFOS) (1000 μg kg^-1) soil and copper (Cu) (500 mg kg^-1) soil were also used to understand the interactions of particulate plastics and contaminants in relation to C dynamics. After two weeks of the incubation period, soil respiration, MBC, dehydrogenase activity (DHA), and microbial C use efficiency (CUE) were measured. The DHA, MBC, and microbial CUE values were less in contaminated soil treatments than pristine soil, thereby revealing the influence of environmental stress on decreased microbial activity. The microbial activity as measured by the above parameters was higher in the presence than absence of particulate plastics addition. In the Cu-contaminated soil, the CUE was significantly (p < 0.01) higher in particulate plastics treated soils than untreated soils. Moreover, improvement of CUE was observed when particulate plastics were added to the PFOS contaminated soils than control soils. The interactions of particulate plastics with organic and inorganic contaminants were effective in modulating their toxicity to soil microbial function, thereby affecting the SOC storage. Finally, a field study was conducted on two texturally different soils to determine the influence of biosolids application on selected soil chemical properties and CO₂ fluxes. Two sites, located in Manildra (clay loam) and Grenfell (sandy loam), in Australia, were treated at a single level of 70 Mg ha^-1 biosolids. Soil samples were analyzed for SOC fractions. Liquid-state ¹³C and ¹H NMR spectroscopy and FT-IR techniques were used to understand the major constituents present in the humic acid fractions. The natural abundances of soil δ¹³C and δ¹⁵N were measured as isotopic tracers to fingerprint C derived from biosolids. In-situ diurnal CO₂ fluxes, soil moisture, and temperature were also measured using an automated LI-COR LI-8100A soil respirometer. Application of biosolids increased the surface (0–15 cm) SOC by > 45% at both sites, which was attributed to the direct contribution from residual C in the biosolids and also from the increased biomass production. At both sites, application of biosolids increased the non-labile C fraction which indicated the SOC storage potential of biosolids. The spectroscopy results revealed a predominance of aliphatic characteristics in humic acids in biosolids treated soils compared to control soils. Soils amended with biosolids showed depleted δ¹³C, and enriched δ¹⁵N indicating the accumulation of biosolids residual C in soils. The CO₂ flux data indicated that the addition of biosolids was effective in building SOC in both the clay loam and sandy loam soils. In conclusion, the meta-analysis and the field experiments provided evidence for the land application of biosolids as a sustainable strategy to store C in soils. Co-composting biosolids with nanoclay and alkaline materials was found to be suitable for SOC stabilization in soil. Interactions of particulate plastics in biosolids with organic and inorganic contaminants modulated their toxicity to soil microbial activity, thereby improving microbial C use efficiency and SOC storage. The field-based CO₂ flux data indicated that the addition of biosolids was effective in building SOC in soils.
Subject: biosolids; soil organic carbon; carbon fractions; climate change mitigation; soil δ¹³C; soil δ¹⁵N
Identifier: http://hdl.handle.net/1959.13/1392729
Identifier: uon:33451
Language: eng
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