Mineralization Rate Constant Research Articles

Abatement of algal extracellular organic matter by vacuum ultraviolet: Effect of dissolved oxygen and role of in-situ formed reactive oxygen species

Algal extracellular organic matter (EOM) in water produced during the outbreak of algal blooms is difficult to be effectively removed by conventional water treatment processes. Compared with ultraviolet (UV), vacuum ultraviolet (VUV) can additionally radiate 185 nm photons, and VUV can split water to produce reactive oxygen species (ROS) in-situ. Herein, abatement and characteristic variation of EOM under VUV irradiation and the mechanism were investigated. Results indicated that EOM abatement by VUV irradiation were significantly higher than that by UV irradiation. The mineralization rate constant of EOM under VUV was 2.25 times of that under UV. Besides, under VUV irradiation, the abatement efficiency of EOM was promoted with the increased dissolved oxygen (DO), and EOM with a lower initial concentration had a higher abatement efficiency. Intensities of characteristic fluorescence peaks of EOM decreased obviously after VUV irradiation, and removal rates of specific fluorescent organic components were ≥ 74.4%. Under VUV irradiation, organic matter in EOM with higher molecular weight was transformed into that with lower molecular weight. Moreover, hydroxyl radical (•OH) generated in-situ by VUV dissociating water with different DO was directly identified by fluorescence molecular probe technology, and the higher DO caused the higher production of •OH. Furthermore, the mechanism of EOM abatement by VUV was proposed. DO and the produced ROS enhanced the abatement efficiency of EOM, and they played important roles in EOM abatement. This study disclosed abatement characteristics of EOM under VUV irradiation and provided great value for expanding the utilization of VUV in water treatment.

Invasive Spartina alterniflora alters sediment organic carbon mineralization dynamics in a coastal wetland of Southeastern China

Invasive Spartina alterniflora has significant impacts on sediment carbon pool and turnover in the tidal wetlands of estuaries and coasts. Yet, how this exotic S. alterniflora affects sediment organic carbon mineralization dynamics remains poorly understood. In this study, sediment geochemical properties, organic carbon fractions, and mineralization dynamics were examined in a native Cyperus malaccensis habitat and three invasive S. alterniflora habitats (6-, 10-, and 14-year-old) in summer and winter. We found that invasive S. alterniflora generally increased sediment total organic carbon and their labile fraction contents. The organic carbon mineralization rates and cumulative carbon mineralization amounts were significantly influenced by invasive S. alterniflora, and their values increased with this exotic plant invasion chronosequences. The mineralization rates and cumulative mineralization amounts were also characterized by higher values in surface sediment (0 – 10 cm depth) compared to subsurface sediment (10 – 20 cm depth) and by seasonal variations with higher values in summer than in winter. The sediment organic carbon labile fractions, rather than total organic carbon, were the most important factor affecting carbon mineralization dynamics. The cumulative carbon mineralization amounts exhibited an excellent fit to the first-order kinetic equation (R2 ≥ 0.93). The changes in modeled kinetic parameters (potential carbon mineralization amounts (C0) and carbon mineralization rate constant (k)) among these four habitats were similar to carbon mineralization rates, implying invasive S. alterniflora promoted the availabilities of organic compounds for microbial respiration metabolism. Overall, our findings highlighted the importance of S. alterniflora invasion in accelerating organic carbon decomposition and carbon dioxide release potential, although it also increases carbon accumulation.

Drivers for soil organic carbon stabilization in Elbe River floodplains

AbstractBackgroundFloodplains play an important role in the global carbon (C) cycle, particularly due to their large soil organic carbon (SOC) storage potential. However, a heterogeneous microrelief and anthropogenic landscape modifications complicate the understanding of stabilization processes of SOC in floodplains.AimDetermining the predominant drivers for SOC stabilization in Elbe River floodplain soils.MethodsWe measured SOC density fractions, microbial biomass, and mineralization characteristics in top‐ and subsoils of eight floodplain sites of the lower middle Elbe River.ResultsThe heavy fraction (HF) was the most important SOC pool, with a contribution of >64% at both depth intervals. With soil depth, HF pool size increased and the occluded light fraction (oLF) decreased, whereas the free LF (fLF) stayed the same. The contribution of the HF to SOC was positively related to fine texture (R2 = 0.64). Mineralizable C was negatively related to fine texture at both depth intervals. Both results suggest a positive effect of fine texture on SOC stabilization. The metabolic quotient was related to the amount of available SOC in the topsoil, but no relation was found in the subsoil. However, in top‐ and subsoil, the mineralization rate constant was positively related to the C/N ratios of the fLF and the oLF, indicating that the quality of fresh plant litter is an important energy source for microbial mineralization.ConclusionSedimentation of fine‐textured material is the most important driver for SOC stabilization rather than fresh plant litter input. Thus, SOC stabilization strongly depends on relief, flooding, and sedimentation.

Mineral composition controls the stabilization of microbially derived carbon and nitrogen in soils: Insights from an isotope tracing model

AbstractEvidence is emerging that microbial products and residues (necromass) contribute greatly to stable soil organic matter (SOM), which calls for the necessity of separating the microbial necromass from other SOM pools in models. However, the understanding on how microbial necromass stabilizes in soil, especially the mineral protection mechanisms, is still lacking. Here, we incubated 13C‐ and 15N‐labelled microbial necromass in a series of artificial soils varying in clay minerals and metal oxides. We found the mineralization, adsorption and desorption rate constants of necromass nitrogen were higher than those of necromass carbon. The accumulation rates of necromass carbon and nitrogen in mineral‐associated SOM were positively correlated with the specific surface area of clay minerals. Our results provide direct evidence for the protection role of mineral in microbial necromass stabilization and provide a platform for simulating microbial necromass separately in SOM models.

Mineralization mechanism of organic carbon in maize rhizosphere soil of soft rock and sand mixed soil under different fertilization modes.

This article endeavors to investigate the influence of various fertilization methods on the characteristics of rhizosphere soil and organic carbon mineralization in the mixed soil of Mu Us Sandy land under maize cultivation, with the objective of laying the groundwork for low-carbon agriculture and the development of high-quality farmland. The research focuses on soft rock and sand composite soil with a 1:2 ratio, and it comprises four treatments: no fertilization (CK), only chemical fertilization (CF), only cattle manure application (MF), and only oil residue application (DF). The findings revealed that the use of organic fertilizer substantially elevated nutrient content and enzyme activity in the maize rhizosphere soil. Furthermore, it had a notable influence on both soil aggregate diameter and stability. Specifically, the DF treatment led to a significant increase in both soil aggregate diameter and stability. The mineralization rate of organic carbon in the maize rhizosphere soil could be categorized into two distinct phases: a rapid initial decline followed by a slower release. By the end of the incubation period, the cumulative mineralization of organic carbon in the MF, DF, and CF treatments showed a significant increase of 119.87%, 57.57%, and 24.15%, respectively, in comparison to the CK treatment. Additionally, the mineralization rate constants of the DF and MF treatments experienced a substantial rise, with increments of 23.52% and 45.97%, respectively, when contrasted with the CK treatment. The bacterial phyla Actinobacteriota, Proteobacteria, Chloroflexi, Acidobacteriota, and Firmicutes were dominant in the rhizosphere soil bacterial community. Specific genera such as Nocardioides and Sphingomonas showed significant correlations with organic carbon mineralization. The application of different organic fertilizer can improve soil physical, chemical and biological properties, and promote the mineralization process of organic carbon in maize rhizosphere soil. Notably, the DF treatment exhibited the most favorable outcome, improving the overall quality of maize rhizosphere soil while incurring a minimal loss of unit organic carbon. These findings hold significant implications for optimizing field management practices and augmenting soil quality.

Gross nitrogen mineralization and nitrification at an optimal phosphorus input level in southern Chinese red soil with long-term fertilization

In China, phosphorus (P) is recognized as a “key limiting nutrient” for crop production, and its overuse results in underground leaching, ecosystem alterations and risks to humans, such as degraded surface water quality. The coupling of nitrogen (N) and P implies that soil N dynamics are largely affected by P availability. However, how the addition of P affects soil N transformations remains less understood. To determine the optimal P-input level, we performed an incubation experiment on an upland soil from Jinxian in China after long-term mineral fertilizer application and P addition. The two treatments without N addition T1 (no fertilizer) and T2 (inorganic potassium fertilizer) and the two treatments with N addition T3 (inorganic nitrogen fertilizer) and T4 (inorganic nitrogen and potassium fertilizer) were selected from the long-term experiment that involved scientific management at five P-input levels (0, 25, 50, 75, and 100 kg P2O5 ha−1) with three replications. The results showed that soil organic matter (SOM) increased in the T3 and T4 treatments compared with the T1 and T2 treatments. The T4 treatment resulted in the maximum N concentration of 1.28 g kg−1, followed by that in the T3 treatment (1.25 g kg−1), T2 (0.16 g kg−1) and that in the T1 treatment (0.10 g kg−1), in the soil. Among the different treatments, soil microbial biomass carbon (SMBC) and nitrogen (SMBN) were significantly higher (492.69 mg kg−1 and 73.36 mg kg−1, respectively) in the T3 treatment than in the other treatments, while soil microbial biomass phosphorus (SMBP) was higher in the T4 treatment (17.55 mg kg−1). With the addition of P, the gross N mineralization rate was substantially enhanced when N and K were applied. After the 90-day incubation period, with higher concentrations of NO3--N and NH4+-N in the T4 treatment than in the other treatments, the concentrations were significantly increased by P addition, specifically T4P4 by 11.27% and 37.37%, T4P3 by 12.64% and 30.29%, T4P2 by 22.94% and 64.53%, and T4P1 by 3.93% and 11.09%, compared with those of T4P0, respectively; these results indicated a maximum N mineralization potential (No) and mineralization rate constant, k (NMR). As a result of the increased gross nitrogen mineralization rates and associated NH4+ substrate availability, the gross nitrification rate was also increased by P addition. Based on the polynomial regression analysis, the inclusion of P at the rate of 60 kg P2O5 ha−1 can be used effectively to obtain maximum gross N mineralization rates in soil. Additionally, to fully understand why P addition is more effective under specific soil and environmental conditions, more research is necessary to determine the underlying mechanisms.

Evaluation of nitrogen mineralization under various irrigation water qualities and nitrogen application rates for mulched drip irrigation in an arid region

AbstractUnderstanding the interactive effects of irrigation water quality and fertilization on nitrogen mineralization (Nmin) and accurately predicting Nmin are of great importance for the secure and efficient utilization of brackish water in arid regions. A pot experiment was conducted to determine the Nmin under different drip irrigation water salinities and nitrogen application rates and to modify the nitrogen mineralization potential (N0) and mineralization rate constants (k) of the first‐order kinetic equation of Nmin. An in situ field experiment was conducted to validate the modified equation. The results showed that the amounts of Nmin for water salinities of 1.27, 3.03, and 4.90 g L−1 were 58.9, 76.1, and 45.4 kg ha−1, respectively. Nmin was stimulated when the soil salinities were lower than 6.6, 6.1 and 3.9 g kg−1 for nitrogen application rates of 255, 315 and 375 kg ha−1, respectively. Nitrogen application significantly reduced Nmin. When the nitrogen application rate increased to 375 kg ha−1, the net Nmin rate remained lower, and the effects of salinity on Nmin were attenuated. The Nmin model with modified N0 and k values was developed considering the impacts of soil organic nitrogen, nitrogen application rate, and soil salinity. Model testing indicated that the modified model provided an acceptable estimation of Nmin under field conditions. It will be helpful for developing rational fertilization strategies of drip irrigation with brackish water in arid regions.

High-efficient mineralization of formaldehyde by three-dimensional “PIZZA”-like bismuth molybdate-titania/diatomite composite

The application of TiO2-based photocatalysts in air pollution control has attracted much attention thanks to their advantageous green and sustainable performance. However, how to improve the degradation efficiency under visible light is still challenging. Herein, we report a ternary three-dimensional “PIZZA”-like Bi2MoO6-TiO2/diatomite (BTD) composite with high-efficient mineralization and recycling performance towards gaseous formaldehyde (HCHO) under visible light. The high-efficient adsorption-photocatalysis collaborative system with intimate interface combination is successfully established among Bi2MoO6 (BMO), TiO2 and diatomite. The HCHO mineralization rate constant of BTD-1:2 composite is up to around 4.03 times and 2.18 times higher than those of bare BMO and binary Bi2MoO6-TiO2 composite, respectively. It is indicated that the introduction of diatomite increases active sites and plays the vital role in the improvement of photocatalysis. In addition, the photogenerated holes (h+) and hydroxyl radical (OH) are proved to be the main active species for HCHO mineralization. Furthermore, there is a competitive adsorption relationship between water (H2O) molecules and HCHO molecules, and both H2O molecules and oxygen (O2) molecules participated in the reaction of HCHO mineralization based on in-situ DRIFTs spectra analysis. Our work would give a new perspective on gaseous HCHO purification.

Enhanced visible-light degradation performance toward gaseous formaldehyde using oxygen vacancy-rich TiO2-x/TiO2 supported by natural diatomite

Natural mineral-based composites with outstanding photocatalytic performance have attracted much attention because of their great potential applications in environmental remediation. Herein, we report a natural diatomite supported oxygen vacancy-rich TiO2-x-TiO2 homojunction (TOV-TD composite) photocatalyst for indoor gaseous formaldehyde (HCHO) purification. The designed composite exhibits superior sustainability and mineralization efficiency of HCHO under visible light illumination, which is attributed to the constructed high-efficient adsorption-photocatalysis collaborative system composed of TiO2, TiO2-x and diatomite. In addition, according to the variation of the CO2 concentration in real time, the calculated HCHO mineralization rate constant of TOV-TD-1:3 composite (optimal sample) is up to around 4.42 times that of bare TiO2-x (TOV) and 1.74 times that of TiO2-x-TiO2 (TOV-T) composite, respectively. It is indicated that the introduction of the natural diatomite significantly promotes the content of oxygen vacancies in the composite and provides more adsorption-photocatalysis active centers. Moreover, the hydroxyl radicals (•OH) are proved to be the major active species for HCHO mineralization. This work provides a new composite for constructing adsorption-photocatalysis systems with enhanced visible-light properties for indoor HCHO removal.

Influence of Soil Fertility Management on Nitrogen Mineralization, Urease Activity and Maize Yield

For studying the effect of soil fertility management practices on N mineralization, urease activity and maize yield, replicated field trials were established in 2015 at Misamfu and Msekera agricultural research stations (ARS) representing two geo-climatic regions of Zambia. The soil at Msekera ARS is a sandy clay loam (SCL) from a Paleustult, while that at Misamfu is a loamy sand (LS) from a Kandiustult. The field trials had three categories of treatments namely legumes, traditional and conventional. The legumes group consisted of researcher-recommended legume-cereal intercrop systems of maize with Cajanus cajan, Crotalaria juncea and Tephrosia vogelii in combination with compound D (10% N, 20% P2O5, 10% K2O) and urea (46% N) at the recommended rate (200 kg ha-1) and half of the recommended rate (100 kg ha-1). Composted cattle manure and Fundikila, a special plant biomass management technique, were the inputs under the traditional category. The conventional category consisted of a treatment to which only chemical fertilizer was applied. Urease activity was determined in surface soil samples (0-20 cm) collected from the field trials after 3 years. For N mineralization, a laboratory incubation study was conducted over 13 weeks. For the laboratory incubation, an additional treatment to which no input was applied was included as control. Application of organic inputs significantly increased the potentially mineralizable N (No) by 127% to 256% on the LS and by 51% to 131% on the SCL in comparison to the control. Similarly, the cumulative N mineralized (Ncum) was twice or thrice higher where organic inputs had been applied in comparison to the control. The No followed the order traditional > legumes > conventional > control, while the mineralization rate constant (k) followed the order legumes > conventional > traditional > control on both soils. The rate of N mineralization was significantly higher on the LS than the SCL. Higher rates of chemical fertilizer resulted in high Ncum and higher maize yield. Maize yield was significantly and positively correlated to Ncum, but inversely correlated to the amount of applied N that was mineralized (%Nmin). Urease activity was stimulated by application of organic inputs and suppressed by higher rates of chemical fertilizers. The type of organic inputs; the rate of chemical fertilizers; and soil texture are factors influencing N mineralization and maize yield. Urease activity was largely influenced by the rate of chemical fertilizer, but not the type of organic inputs or soil texture.

Carbon mineralization in subtropical alluvial arable soils amended with sugarcane bagasse and rice husk biochars

Subtropical recent alluvial soils are low in organic carbon (C). Thus, increasing organic C is a major challenge to sustain soil fertility. Biochar amendment could be an option as biochar is a C-rich pyrolyzed material, which is slowly decomposed in soil. We investigated C mineralization (CO 2 -C evolution) in two types of soils (recent and old alluvial soils) amended with two feedstocks (sugarcane bagasse and rice husk) (1%, weight/weight), as well as their biochars and aged biochars under a controlled environment (25 ± 2 °C) over 85 d. For the recent alluvial soil (charland soil), the highest absolute cumulative CO 2 -C evolution was observed in the sugarcane bagasse treatment (1 140 mg CO 2 -C kg -1 soil) followed by the rice husk treatment (1 090 mg CO 2 -C kg -1 soil); the lowest amount (150 mg CO 2 -C kg -1 soil) was observed in the aged rice husk biochar treatment. Similarly, for the old alluvial soil (farmland soil), the highest absolute cumulative CO 2 -C evolution (1 290 mg CO 2 -C kg -1 soil) was observed in the sugarcane bagasse treatment and then in the rice husk treatment (1 270 mg CO 2 -C kg -1 soil); the lowest amount (200 mg CO 2 -C kg -1 soil) was in the aged rice husk biochar treatment. Aged sugarcane bagasse and rice husk biochar treatments reduced absolute cumulative CO 2 -C evolution by 10% and 36%, respectively, compared with unamended recent alluvial soil, and by 10% and 18%, respectively, compared with unamended old alluvial soil. Both absolute and normalized C mineralization were similar between the sugarcane bagasse and rice husk treatments, between the biochar treatments, and between the aged biochar treatments. In both soils, the feedstock treatments resulted in the highest cumulative CO 2 -C evolution, followed by the biochar treatments and then the aged biochar treatments. The absolute and normalized CO 2 -C evolution and the mineralization rate constant of the stable C pool ( K s ) were lower in the recent alluvial soil compared with those in the old alluvial soil. The biochars and aged biochars had a negative priming effect in both soils, but the effect was more prominent in the recent alluvial soil. These results would have good implications for improving organic matter content in organic C-poor alluvial soils.

Nitrogen Mineralization, Soil Microbial Biomass and Extracellular Enzyme Activities Regulated by Long-Term N Fertilizer Inputs: A Comparison Study from Upland and Paddy Soils in a Red Soil Region of China

A long-term experiment (38 years) was conducted to elucidate the effects of long-term N addition on the net N mineralization in both paddy and upland soils, based on their initial soil N status, with and in connection with soil microbial biomass and N cycling extracellular enzyme activities. Two treatments without N addition CK (No fertilizer) and K (inorganic potassium fertilizer) and two treatments with N addition (inorganic nitrogen fertilizer) and NK (inorganic nitrogen and potassium fertilizer) were placed in incubation for 90 days. Results showed that the total N and soil organic carbon (SOC) contents were higher in the treatments with N application compared to the treatments without N in both paddy and upland soils. The SOC content of paddy soil was increased relative to upland soil by 56.2%, 45.7%, 61.1% and 62.2% without N (CK, K) and with N (N and NK) treatments, respectively. Site-wise, total N concentration in paddy soil was higher by 0.06, 0.10, 0.57 and 0.60 times under the CK, K, N and NK treatments, respectively, compared with upland soil. In paddy soil, soil microbial biomass nitrogen (SMBN) was higher by 39.6%, 2.77%, 29.5% and 31.4%, and microbial biomass carbon (SMBC) was higher by 11.8%, 11.9%, 10.1% and 12.3%, respectively, in CK, K, N and NK treatment, compared with upland soil. Overall, compared to upland soil, the activities of leucine-aminopeptidase (LAP) were increased by 31%, 18%, 20% and 11%, and those of N-acetyl-b-D-glucosaminidase (NAG) were increased by 70%, 21%, 13% and 18% by CK, K, N and NK treatments, respectively, in paddy soil. A significantly linear increase was found in the NO3−-N and NH4+-N concentrations during the 90 days of the incubation period in both soils. NK treatment showed the highest N mineralization potential (No) along with mineralization rate constant, k (NMR) at the end of the incubation. SMBC, SMBN, enzyme activities, NO3−-N and NH4+-N concentrations and the No showed a highly significant (p ≤ 0.05) positive correlation. We concluded that long-term N addition accelerated the net mineralization by increasing soil microbial activities under both soils.

A ternary CdS/AgBr/Ag3PO4 nanocomposite: characterization and the kinetics of its photocatalytic activity.

A ternary CdS/AgBr/Ag3PO4 coupled system was prepared, characterized by different techniques, and used for the photodegradation of methylene blue (MB). The hexagonal (wurtzite) CdS, the cubic AgBr, and the Ag3PO4 body-centered cubic crystallite phases were detected by XRD patterns. The Scherer equation showed the crystallite sizes of 3, 26.3, 28, and 27.9 nm for CdS, Ag3PO4, AgBr NPs, and the ternary CdS/AgBr/Ag3PO4 sample, while the Williamson-Hall model got the values of 1.8, 46.2, 62.12, and 92.44 nm, respectively. The diffuse reflectance spectra (DRS) showed that the ternary catalyst could absorb the whole range of visible light photons. The photoluminescence (PL) spectra significantly depended on the solvent nature, and the sharp scattering peaks appeared in the water, while these were absent in acetone as solvent. The ternary catalyst also showed a lower PL intensity and a higher photocatalytic activity concerning the individual NPs. When the moles of CdS were three times greater than the other components, the resulted ternary catalyst showed the lowest PL intensity and the highest degradation activity. The MB mineralization was also studied by the COD technique and compared with MB photodegradation kinetically. The MB photodegradation rate constant of about 0.0276 min-1 (correspond to t1/2 25.1 min) was 1.75 times greater than the MB mineralization rate constant (about 0.0158 min-1 correspond to t1/2 value of 43.9 min).

Study of the photocatalytic activity of CdS–ZnS nano-composite in the photodegradation of rifampin in aqueous solution

The elimination of rifampin (RN) as a pollutant from an aqueous solution was performed via the photodegradation process by the coupled CdS–ZnS system under visible light irradiation. The catalyst was briefly characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and transmission electron microscope (TEM) techniques. The cubic ZnS structure and the hexagonal CdS structure with the crystallite size of 10 nm were detected from the XRD patterns. From the DRS results, the bandgap energies of 2.3, 3.9, and 2.4 eV were obtained for CdS, ZnS, and CdS–ZnS, respectively. The pH-values of 5.2 (5.25), 5.8 (5.8), and 5.9 (5.88) were obtained for the pHpzc of CdS, ZnS, and CdS–ZnS by two methods, respectively. Increased photocatalytic activity of the coupled ZnS–CdS system was achieved compared to the single systems and when the moles of CdS is 6 times higher than the ZnS component, the best activity was obtained. The optimal degradation conditions were the catalyst dose: 0.5 g/L, CRN: 8 mg/L, pH: 2, and irradiation time: 120 min. The rate constants of RN photodegradation and mineralization (from the chemical oxygen demand (COD) results) were 0.028 and 0.019 min−1, respectively. The mechanism pathway was similar to the type (II)-heterojunction system in which the accumulated holes in VB-ZnS, the accumulated electrons in CB-CdS, and hydroxyl radicals are more important reactive species in the photodegradation of RN molecules. Further, this mechanism is useful for hydrogen production by both the photogenerated electrons in CB-CdS and CB-ZnS positions. Another mechanism that can illustrate the photodegradation process is similar to the direct Z-scheme mechanism pathway in which the accumulated electrons in the CB-ZnS, the accumulated holes in the VB-CdS, and the superoxide radicals are more important active centers for the degradation of RN molecules. Also, the accumulated holes in the CB-CdS position are another active center to oxidize RN molecules. Besides, the accumulated holes in the CB-ZnS position are more suitable for hydrogen production. The photogenerated holes in the CB-CdS position are also capable to oxidize water molecules for oxygen evolution.

Removal of sulfamethizole from aqueous solution using advanced oxidation processes: effects of pH and salinity.

This study investigates the removal of sulfamethizole (SFZ) in ozone (O3), O3/Na2S2O8 (sodium persulfate), UV/Na2S2O8, UV/O3, and UV/O3/Na2S2O8 systems. The effects of pH and salinity on SFZ mineralization were evaluated. The mineralization of SFZ followed pseudo-first-order kinetics. At pH 5, the rate constants of SFZ mineralization in O3, O3/Na2S2O8, UV/Na2S2O8, UV/O3, and UV/O3/Na2S2O8 systems were 0.576, 0.924, 0.702, 1.26, and 5.21 h-1, respectively. The SFZ mineralization rate followed the order pH 5 > pH 7 > pH 9 in all tested advanced oxidation processes. Salinity increased the rate of SFZ mineralization in O3 and O3/Na2S2O8 systems and decelerated it in UV/Na2S2O8, UV/O3, and UV/O3/Na2S2O8 systems. UV/O3/Na2S2O8 was the best system for mineralizing SFZ, and sulfate radicals were the predominant species in UV/O3/Na2S2O8.

The coupled AgI/BiOI catalyst: Synthesis, brief characterization, and study of the kinetic of the EBT photodegradation

The relatively novel AgI/BiOI coupled system (CS) was prepared in-situ by mechanical mixing of the as-synthesized AgI and BiOI nanoparticles (NPs) and characterized by various characterization techniques such as XRD, SEM-EDX, and UV–Vis DRS. XRD results showed the hexagonal crystals of AgI and the tetragonal crystals of BiOI in the CS. The grain sizes of 34.1 and 25.6 nm were estimated for the CS by the Scherrer and Williamson-Hall equations, respectively. The bandgap values of 2.7, 1.75, and 1.83 were estimated based on absorption edge wavelengths for AgI, BiOI, and CS samples, respectively. The CS showed a boosted photocatalytic activity towards Eriochrome Black T (EBT). This boosted activity depends on the amounts of the CS-ingredients and the CS with an AgI:BiOI mole ratio of 1:2 showed the highest activity. The photodegradation rate constant of 0.0167 min−1 with a t1/2 value of 41.5 min was obtained from the Hinshelwood plot. Further, the mineralization rate constant of 0.0137 min−1 with a t1/2 value of 50.6 min was obtained by applying the COD results in the Hinshelwood model.

Organic Inputs and Chemical Fertilizer on Carbon Mineralization From Two Ultisols

There are challenges that limit the use of organic inputs for soil fertility management. Amongst them is the limited knowledge of factors that affect rates of decomposition and nutrient release from different organic inputs. A study was conducted on surface soil samples of two Ultisols to determine factors affecting carbon (C) mineralization from selected organic inputs. A loamy sand (LS) from a Kandiustult and a sandy clay loam (SCL) from a Paleustult were used. Fine earth fractions of the soils mixed with organic inputs with and without chemical fertilizer were incubated for 13 weeks and the CO2 evolved was measured. Organic inputs used were biomasses of Cajanus cajan, Tephrosia vogelii, Crotalaria juncea, Mucuna pruriens, a mixture of native grasses and shrubs and composted cattle manure. The latter two inputs are traditionally used by farmers, while the leguminous plants were recommended by scientists. Treatments with chemical fertilizer only, representing the conventional farming practice, and a control with soil alone were included. Addition of organic inputs with or without fertilizer increased total CO2 emissions by 81 to 129% on the LS and by 18 to 34% on the SCL. Adding chemical fertilizer significantly (p < 0.05) increased C mineralization rate constant (k) by 116% on the LS and 48% on the SCL. The mean residence time of organic carbon from treatments grouped by input type followed the order: Control > Traditional > Legumes > Conventional on both soils. In general, the k on the LS was double that on the SCL. The type of organic input, soil texture and application of chemical fertilizer significantly affected C mineralization rates from the soils.

Soil microbial biomass and extracellular enzymes regulate nitrogen mineralization in a wheat-maize cropping system after three decades of fertilization in a Chinese Ferrosol

Soil net nitrogen (N) mineralization is a vital process that impacts the global N cycling and regulates the N availability for plant development. The objectives of this study were to evaluate the response of N mineralization to long-term organic versus inorganic fertilization and to quantify the relationships between N mineralization and soil microbial characteristics in the ferrosol (red soil) of South China after 30 years of mineral and manure application in a wheat-maize cropping system. Soil was sampled from a wheat-maize rotation system, consisting of five treatments. The treatments included (1) CK (no fertilizer), (2) PK (synthetic phosphorus and potassium fertilizer), (3) NK (synthetic nitrogen and K fertilizer), (4) N (synthetic N fertilizer), and (5) NPKM (synthetic NPK fertilizer and manure). The sampled soil was analyzed for physicochemical parameters and incubated for the determination of N mineralization, soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and associated soil enzymes related to C and N cycling. Results showed that NPKM increased soil organic carbon (SOC), available P (AP), total P (TP), and total nitrogen (TN) by 132%, 880%, 293%, and 76% respectively, over the control (CK). Among different treatments, soil microbial biomass nitrogen (SMBN) and carbon (SMBC) were highest under the NPKM treatment. N-cycling and P-cycling enzyme activities also showed significant differences among treatments. N-Acetyl-β-d-glucosaminidase (NAG), leucine-aminopeptidase (LAP), and acid phosphatase (AcP) activities were also highest under the NPKM treatment, at 650.36, 32.36, and 23.41 (mol g−1 h−1), respectively. A linear increase was observed in the NO3−-N and NH4+-N concentrations throughout the 90-day incubation period. NPKM showed a maximum N mineralization potential (No) and mineralization rate constant, k (NMR), at the end of the incubation period. A principal component analysis (PCA) interpreted the differences among fertilization and their effects on net N mineralization. A significant (p ≤ 0.05) positive correlation was observed between SMBC (R2 = 0.87), SMBN (R2 = 0.92), enzyme activities, and the No. Structural equation modeling (SEM) revealed that SOC, TN, and TP directly affected mineralization, while SMBC and SMBN indirectly affected the net mineralization. Manure input increased the extracellular enzymes in soil, which accelerated the net N mineralization due to enhanced soil microbial activities. Consequently, long-term manure addition appears to be an optimal approach to meet the nutrient demands and to enhance the N availability in a wheat-maize cropping system.

Ultrasound Enhanced Activity of Catalytic Ozonation for Degradation of 2-sec-butyl-4,6-dinitrophenol in Aqueous Solution and Wastewater

The degradation and mineralization of 2-Sec-butyl-4,6-dinitrophenol (DNBP) in the aqueous solution was investigated by various advanced oxidation processes including US, US/TiO2, O3, O3/TiO2, O3/US, and US/O3/TiO2. The obtained results revealed that all processes obeyed pseudo-first-order kinetics and the coupled US/O3/TiO2 process was the most efficient method for the removal of the pollutant with a high synergistic effect. Then, the effect of major operational parameters, such as the initial DNBp concentration, ozone, and TiO2 dosage, US power, and pH, on the efficiency of the significant coupled process was studied. Total organic carbon (TOC) was applied for monitoring the mineralization and lower rate constants were obtained and compared to the degradation rate constants. Finally, four degradation intermediates were identified by the GC-MS method and the mineralization of petrochemical wastewater was monitored by Chemical Oxygen Demand (COD) under optimized conditions.

The relationship between bacterial diversity and organic carbon mineralization in soft rock and sand compound soil.

The soil organic carbon (SOC) mineralization rate in sandy soil plays an important role in improving soil quality, and a research is needed to determine management practices that optimize the mineralization rate. When sandy soil is improved by adding soft rock, the specific promotion process of bacterium to SOC mineralization remain unclear. To investigate these mechanisms, we selected four treatments with soft rock to sand volume ratios of 0:1 (CK), 1:5 (C1), 1:2 (C2) and 1:1 (C3) to study. The mineralization rate of organic carbon was measured using the lye absorption method. High-throughput sequencing and scanning electron microscopy were used to determine the bacterial community structure and soil microstructure, respectively. The results showed that the organic carbon content of the sandy soil increased significantly (182.22-276.43%) after using the soft rock treatments. The SOC mineralization rate could be divided into two stages: a rapid decline during days 1-8 and a slow decline during days 8-60. With increased incubation time, the intensity of the cumulative release of organic carbon gradually weakened. Compared with the CK treatment, the SOC mineralization accumulation (Ct) and the potential mineralizable organic carbon content (C0) in the C1, C2, and C3 treatments increased significantly, by 106.98-225.94% and 112.22-254.08%, respectively. The cumulative mineralization rate (Cr) was 18.11% and 21.38% smaller with treatments C2 and C3, respectively. The SOC mineralization rate constant (k) decreased significantly after the addition of soft rock, while the half-turnover period (Th) changed inversely with k. Compared with the CK treatment, the number of gene copies of the soil bacteria increased by 15.38-272.53% after adding soft rock, with the most significant increase in treatment C3. The bacterial diversity index also increased significantly under treatment C3. The three dominant bacteria were Proteobacteria, Actinobacteria, and Chloroflexi. The correlation between Cr and one of the non-dominant bacteria, Firmicutes, was large, and the bacteria had a significant positive correlation with k. At the same time, the abundance of Firmicutes under treatments C2 and C3 was small. As the proportion of soft rock increased, the soil particles changed from point contact to surface contact, and the adhesion on the surface of the particles gradually increased. Results from this study show that the retention time of SOC can be increased and the carbon sequestration effect is better when the ratio of soft rock to sand is set to 1:2.