Hydrochars derived from sewage sludge: effects of pre-treatment with water on char properties,phytotoxicity and chemical structure

Large amounts of labile compounds are adsorbed to the surface of chars produced by hydrothermal carbonization (HTC). The aim of this study was to characterize the core and adsorbed fractions of hydrochars and to gain knowledge about the possibility to remove phytotoxic compounds by washings with water. Chars were produced by HTC of sewage sludge at different temperatures (180 – 200 °C) and over different periods of time (4 – 8 h). For comparison one pyrolysis char produced by thermocatalytic low temperature conversion (LTC) at 400 °C for 1 h was included in the study. The chars and their feedstocks were treated varying the duration (1 x 15, 1 × 30 and 1 × 60 min) and number (2 x 60 and 3 × 60 min) of washings. Physicochemical properties, including the molecular structure of the test materials, and their effects on germination and plant growth were analysed. Element concentrations and phytotoxic effects were reduced and the number of washings had a stronger effect than their length of time. Intensive washings with water reduced the hydrochars’ portion of biodegradable compounds significantly. However, also plant available nutrients were lost by washing with water, decreasing the value of hydrochars as a soil amendment.     

Effect of Organic Residues and Their Derived Biochars on the Zinc and Copper Chemical Fractions and Some Chemical Properties of a Calcareous Soil

ABSTRACT

Addition of more resistant organic materials, such as biochars, to soils not only enhances soil C sequestration but also can also benefit soil fertility. The aim of this study was to investigate the effect of two organic materials (sheep manure and vermicompost) and their biochars produced at two pyrolysis temperatures (300 and 500°C) applied at 5% (w/w) on the chemical fractions of Zn and Cu and some chemical characteristics of an unpolluted, light textured calcareous soil. Addition of the raw organic materials and their-derived biochars significantly enhanced plant available K, P, and Zn but significantly decreased plant available Cu in the soil. Sheep manure biochar produced at 300°C was most effective at increasing plant available P (13-fold) and K (1.9 fold) likely due to formation of more soluble forms of P and K compared to raw material or biochar produced at higher temperature (500°C). Whereas, raw vermicompost and sheep manure were most effective at enhancing plant available Zn, by increasing water soluble and exchangeable Zn fraction likely due to organic complexation. All amendments, especially biochars produced at 300°C reduced water soluble and exchangeable Cu mainly attributed to increased soil P availability. The results of this study showed that in the short-term, addition of the low-temperature biochars was best for enhancing soil P and K availability, but concomitantly reduced Cu availability the most, whereas, addition of the raw organic materials was better for enhancing Zn availability compared to the biochars.     

Quick Fiber Process: Effect of Mash Temperature,Dry Solids,and Residual Germ on Fiber Yield and Purity

Preliminary calculations showed that recovery of fiber before fermentation in the dry grind ethanol facilities known as the Quick Fiber process increases fermenter capacity and reduces ethanol production cost by as much as 4 ¢/gal. The objective of the current research was to evaluate the effect of mash temperature, dry solids, and residual germ on fiber yield and purity when using the quick fiber process. Fiber was recovered by flotation and skimming, while maintaining a specified temperature, dry solids, and residual germ in the mash. Varying temperature and dry solids in the mash resulted in a statistically significant effect on the fiber yield, neutral detergent fiber (NDF) content, and weight of NDF/100 g of dry corn. Varying residual germ in the mash resulted in statistically significant differences for NDF through dilution and the weight of NDF/100 g of dry corn. The highest fiber yield was 10.9% at 45°C, 23% dry solids, and 15% residual germ; the highest NDF was 50.9% at 30°C, 21% dry solids, and 0% residual germ. The highest weight of NDF/100 g of dry corn was observed at 45°C, 23% dry solids, and 0% residual germ.     

土壤呼吸对生物炭添加的短期响应：发酵后处理和无机氮的影响

The biodegradability of chars derived from pyrolysis and hydrothermal carbonisation (HTC) was studied in short-term dynamic incubation experiments under controlled conditions. Carbon dioxide C (CO$_{2}$) emissions from soil-char mixtures in combination with solid digestate or mineral nitrogen (N) fertiliser were measured in dynamic chambers for 10 d.~Compared to the original material (maize straw), pyrolysis and HTC chars showed significantly lower CO$_{2}$ emissions and slower decay dynamics; and compared to the soil control, HTC char increased soil respiration to a significant extent, while pyrolysis char did not. The addition of mineral N resulted in a delayed respiration dynamics for HTC char, while the addition of digestate resulted in an increase in the respired CO$_{2}$ for pyrolysis char and a decrease for HTC char. For the first time, a peculiar two-stage decay kinetics was observed for HTC char, indicating a highly inhomogeneous substrate consisting at least of two C pools.     

Effects of irrigation volumes and organic fertilizers on eggplant grown in Mediterranean environment

A three-year field experiment was carried out in Mediterranean conditions to study the effects of different irrigations and organic fertilizers on yield, quality and nitrogen utilization of eggplant crop and on soil properties. In a split-plot design, two irrigation treatments (re-establishing 100% and 50% of the calculated maximum evapotranspiration) and four fertilizer treatments (mineral fertilizer, commercial stable manure, anaerobic digestate and municipal solid waste compost) were compared. The highest water volume increased significantly the total and marketable yield, the number of marketable fruits, the dry matter of fruits and the nitrogen-use efficiency with respect to the treatment with the lowest irrigation. Nevertheless, the same treatment decreased significantly the fruit dry matter percentage and total soluble solid content. The lowest water volume led to an improvement of fruit quality. Anaerobic digestate increased significantly the total and marketable yield and dry matter compared with compost. Harvest index, nitrogen harvest index, pH, acidity and total soluble solids did not show significant differences among all fertilizer treatments. N translocation ability of plants and fruit quality were not influenced by the type of fertilizer. At the end of experiment, anaerobic digestate and compost reached the highest levels of soil total organic carbon and humic and fulvic acids content. Besides, anaerobic digestate increased the total extractable carbon, phosphorus and nitrogen content compared to all other treatments. Soil copper, nickel and lead content in all treatments enhanced compared to that at the beginning of experiment, but this accumulation did not represent a possible environmental risk. The content of heavy metals in the soil, after 3 years of application, did not exceed the limits imposed by the Italian law. This study showed that the organic wastes, after being adequately processed, could be applied successfully in agriculture especially in arid environments, characterized by quick mineralization and very low organic matter content.     

The effect of preplant nitrogen and soil temperature on yield and nitrogen accumulation of alfalfa 1

Abstract

Recommendations for the use of preplant N in alfalfa establishment are controversial. Growth chamber experiments were conducted to examine the effect of preplant N and soil temperature on yield and N accumulation of alfalfa (Medicago sativa L.). Alfalfa was grown in river sand at three day/night soil temperatures (18/12°C, 24/16°C, and 27/21°C), and at five levels of preplant N (0, 10, 20, 40, 80 kg ha^?1). At 18/12°C, 40 kg ha^?1 preplant N resulted in a 69% increase in shoot dry matter yield. Dry matter and N accumulation rates were greatest at 40 and 80 kg ha^?1. Preplant N effects on dry matter and N accumulation at 18/12°C were expressed primarily between the early bud and early flowering stages. Assessment of soil temperature and soil N availability is necessary to determine the potential for a yield response of alfalfa to preplant N.     

Extraction of Wheat Starch with Aqueous Sodium Hydroxide

Wheat starch was extracted with aqueous sodium hydroxide at 30–38% starch solids, pH 11.5–12.3, and 25–42°C for 0.17–24 hr. Stirring wheat starch at pH 12.3 and 25°C for 3 and 24 hr, then washing with water, neutralizing, and washing again, removed 70 and 90% phosphorus (P), respectively. Adding 16% sodium sulfate (dry starch basis) into the alkaline medium removed ≈80% of P at pH 12.0 and 25°C in 3 hr and >95% of P at pH 11.7 and 42°C in 3 hr. Sulfate ion was absorbed strongly by wheat starch in aqueous sodium hydroxide at pH 12.0, and sodium sulfate also increased the starch's uptake of hydroxide ion. Low-P wheat starch (>90% of P removed) retained the fatty acids in the untreated starch, but a fatty acid-amylose complex was not detectable by differential scanning colorimetry. The enthalpy of gelatinization of the low-P wheat starch almost matched that of prime starch, as did its X-ray diffraction pattern. Those data are consistent with saponification of the lysophospholipid in the amorphous phase of the starch to form fatty acid salts and glycerol-choline or glycerol-ethanolamine phosphodiesters that slowly diffused out of the granules. The low-P wheat starch was judged to have less “cereal” odor than the prime starch, and its pasting temperature at 9.3% starch solids was lowered by ≈10°C.     

Influence of soil temperature and soil compaction on growth and P uptake of sugar beet

Sugar beet growth is often impaired by cold and compacted soil. The aim of this study was to determine the effect of soil temperature and soil compaction on the growth and function of sugar beet roots. For this purpose a pot experiment with sugar beet (Beta vulgaris) was conducted in a growth chamber in which the soil temperature was kept constant either at 10°C or 20°C and air temperature at 20°C. The soil was uncompacted (1.30 g cm^?3) or compacted to a bulk density of 1.65 g cm^?3. In order to find out whether growth restriction was caused by insufficient P supply of the plant the experiment was run without and with P application (300 mg per kg soil). Root growth was much smaller at 10°C compared to 20°C, whereas root/shoot ratio was not affected by soil temperature. Hence, root and shoot growth was inhibited to the same extent. P content of the plants was not reduced, neither by cold nor by compacted soil, although parameters of acquisition such as root length and morphological root properties were altered. Soil temperature strongly affected P influx, whereas compaction did not. The calculation with a simulation model showed that at 10°C soil temperature the predicted P uptake of the plants agreed with the measured P uptake irrespective of compaction and P application. However, at 20°C the model underestimated the P influx at low soil P availability even if allowance was made for root hairs. It is concluded that under conditions of high shoot P demand and low P availability in soil P has been mobilized by mechanisms not taken into account by the model.     

Attenuation of Bulk Organic Matter, Nutrients (N and P), and Pathogen Indicators During Soil Passage: Effect of Temperature and Redox Conditions in Simulated Soil Aquifer Treatment (SAT)

Soil aquifer treatment (SAT) is a cost-effective natural wastewater treatment and reuse technology. It is an environmentally friendly technology that does not require chemical usage and is applicable to both developing and developed countries. However, the presence of organic matter, nutrients, and pathogens poses a major health threat to the population exposed to partially treated wastewater or reclaimed water through SAT. Laboratory-based soil column and batch experiments simulating SAT were conducted to examine the influence of temperature variation and oxidation?Creduction (redox) conditions on removal of bulk organic matter, nutrients, and indicator microorganisms using primary effluent. While an average dissolved organic carbon (DOC) removal of 17.7?% was achieved in soil columns at 5?°C, removal at higher temperatures increased by 10?% increments with increase in temperature by 5?°C over the range of 15 to 25?°C. Furthermore, soil column and batch experiments conducted under different redox conditions revealed higher DOC removal in aerobic (oxic) experiments compared to anoxic experiments. Aerobic soil columns exhibited DOC removal 15?% higher than that achieved in the anoxic columns, while aerobic batch showed DOC removal 7.8?% higher than the corresponding anoxic batch experiments. Ammonium-nitrogen removal greater than 99?% was observed at 20 and 25?°C, while 89.7?% was removed at 15?°C, but the removal substantially decreased to 8.8?% at 5?°C. While ammonium-nitrogen was attenuated by 99.9?% in aerobic batch reactors carried out at room temperature, anoxic experiments under similar conditions revealed 12.1?% ammonium-nitrogen reduction, corresponding to increase in nitrate-nitrogen and decrease in sulfate concentration.     

Effect of Broken Corn Levels on Water Absorption and Steepwater Characteristics

Broken corn created by grounding sound corn kernels was added back at levels of 0, 4, 8, 12, or 16%, by weight, to whole kernels of three corresponding hybrids: FR27 × FRMo17 (a soft endosperm corn), FR618 × FR600 (amedium‐hard endosperm corn), and FR618 × LH123 (a hard endosperm corn). The samples had been dried from 28% moisture content to 15% moisture content either by using ambient air at ≈25°C or at 110°C. Samples were steeped for 36 hr at 52°C in 0.15% sulfur dioxide and 0.5% lactic acid steeping solution. The steepwater characteristics, such as water absorption, solids and protein content in the steepwater, and steepwater pH, were measured by periodic sampling and analyzed. Broken corn level has a significant effect on the amount of solids released during steeping and steepwater protein content for all samples. Both steepwater solids and protein content increased linearly as broken corn content increased. Corn drying temperature, kernel hardness, and interactions between drying temperature and kernel hardness has a significant effect on steepwater solids and protein content and steepwater pH in both broken and unbroken corn. Corn dried at low temperature released more soluble solids and protein into the steepwater than corn dried at high temperature. Soft endosperm and medium‐hard endosperm corn released more soluble solids and protein into the steepwater than hard endosperm corn. Soft endosperm corn resulted in a higher steepwater pH than medium‐hard and hard endosperm corn. No significant effect of broken corn content on final moisture content of steeped corn and steepwater pH was observed.     

Application of seaweed and pruning residue as organic fertilizer to increase soil fertility and vine productivity

Algae have an indisputable role in coastal ecosystems, but their accumulation and uncontrolled proliferation cause severe damage for the local municipalities. Fertilization with seaweed has been shown to increase soil fertility and crop production reducing ultimately the need for inorganic fertilizers. However, contradictory results of the compost effect have been reported. In the present work, we aimed at testing the suitability of three composted algae materials obtained in a previous study as soil amendments for vines. The composted materials consisted of pruning waste (P) and seaweed (S) mixed (henceforth, P2S1, P1S1 and P1S2, referring the number to the ratio of P to S). Overall, we observed an increase in soil organic matter, phosphorus (P) and potassium (K) in the soil treated in comparison with soils with inorganic fertilization. A moderate N soil enrichment (ca. 20%) was also detected. The leaf analysis reflected generally the greatest concentrations of NPK for the organic treatments, but this was remarkable only during the first year after seaweed application. A noticeable improvement in grape production was detected especially with the P1S1 compost without compromising grape quality although a decrease in sucrose content was noted with the compost with higher productivity (e.g. P2S1 and P1S1). This slight sucrose drop could be attributable to a greater water availability mediated by the compost or to a dilution factor of the sucrose content caused by a greater number of berries in those vines. These findings suggest that although monitoring of the long-term effects is needed, the use of seaweed amendments for agriculture could offer a cost-effective method for coastal municipalities to reduce excessive algae debris while also minimizing the impacts of inorganic fertilization.     

Hydrochar amendment promotes microbial immobilization of mineral nitrogen

Hydrochars and biochars are products of the carbonization of biomass in different conversion processes. Both are considered suitable soil amendments, though they differ greatly in chemical and physical composition (e.g., aromaticity, inner surface area) due to the different production processes (pyrolysis, hydrothermal carbonization), thus affecting their degradability in soil. Depending on the type, char application may provide soil microorganisms with more (hydrochars) or less (biochars) accessible C sources, thus resulting in the incorporation of nitrogen (N) into microbial biomass. A soil‐incubation experiment was conducted for 8 weeks to determine the relationship between mineral‐N concentration in the soil solution and microbial‐biomass development as well as soil respiration. An arable topsoil was amended with two hydrochars from feedstocks with different total N contents. Biochars from the same feedstocks were used for comparison. Both char amendments significantly decreased mineral‐N concentration and promoted microbial biomass compared to the nonamended control, but the effects were much stronger for hydrochar. Hydrochar application increased soil respiration significantly during the first week of incubation, simultaneous with the strongest decrease in mineral‐N concentration in the soil and an increase in microbial biomass. The amount of N detected in the microbial biomass in the hydrochar treatments accounted for the mineral N “lost” from the soil during incubation. This shows that microbial immobilization is the main sink for decreasing mineral‐N concentrations after hydrochar application. However, this does not apply to biochar, since the amount of N recovered in microorganisms was much lower than the decrease in soil mineral‐N concentration. Our results demonstrate that while both chars are suitable soil amendments, their properties need to be considered to match the application purpose (C sequestration, organic fertilizer).     

The effect of biochar with biogas digestate or mineral fertilizer on fertility,aggregation and organic carbon content of a sandy soil: Results of a temperate field experiment

Substitution of mineral fertilizers with organic soil amendments is postulated to improve productivity‐relevant soil properties such as aggregation and organic matter (OM) content. However, there is a lack of studies analyzing the effects of biochar and biogas digestate versus mineral fertilizer on soil aggregation and OM dynamics under temperate field conditions. To address this research gap, a field experiment was sampled four years after establishment on a sandy Cambisol in Germany where mineral fertilizer or liquid biogas digestate was applied with or without 3 or 40 Mg biochar ha^?1 (produced at 650°C). Soil samples were analyzed for soil organic carbon (SOC) content, pH, cation exchange capacity, bulk density, water‐holding capacity, microbial biomass, aggregate size class distribution, and the SOC content associated with these size classes. 40 Mg biochar ha^?1 significantly increased SOC content in all fractions, especially free particulate OM and the 2–0.25 mm fraction. The yield of small macroaggregates (2–0.25 mm) was increased by biochar, but cation exchange capacity, water‐holding capacity, and pH were not consistently improved. Thus, high‐temperature biochar applied to a sandy soil under temperate conditions is primarily recommended to increase SOC content, which could contribute to climate change mitigation if this C remains sequestered over the long‐term. Fertilizer type did not significantly affect SOC content or other measured properties of the sandy Cambisol, suggesting that replacement of mineral fertilizer with digestate has a neutral effect on soil fertility. Co‐application of biochar with digestate provided no advantages for soil properties compared to co‐application with mineral fertilizer. Thus, independent utilization of these organic amendments is equally suitable.     

Comparison of the hydrolysis characteristics of three polyphosphates and their effects on soil phosphorus and micronutrient availability

Polyphosphate is an alternative phosphorus (P) source which can substitute for orthophosphate‐based P fertilizers in agriculture. In order to explore the effects of polyphosphate addition on soil P availability, and how pH and temperature affect polyphosphate hydrolysis, an aqueous and a soil incubation experiment were conducted at different pHs (5.0 and 8.2) and temperatures (15, 25 and 35°C); the influence of polyphosphate addition on soil available micronutrients (i.e., iron—Fe, manganese—Mn and zinc—Zn) was also studied. The experiments used three different polyphosphate fertilizers (solid and liquid ammonium polyphosphate and polyphosphoric acid) and two soil types (acid and alkaline). In aqueous incubation conditions, the average amount of phosphate () released from polyphosphate fertilizers at 35°C was 2.7 times greater than at 25°C. The average Olsen P in polyphosphate‐treated soil at 35°C was 1.12 times greater than at 25°C, indicating that higher temperature facilitates polyphosphate hydrolysis. Polyphosphate hydrolysis increased as the pH decreased in aqueous solution, but its hydrolysis rate was greater in calcareous soil than in acid soil. Moreover, polyphosphate significantly increased soil available Fe, Mn and Zn concentrations by an average of 14%, 16% and 20%, respectively, relative to orthophosphate fertilizer. In summary, high temperature and low pH favour the hydrolysis of short‐chain polyphosphate (aqueous incubation experiment), and polyphosphate significantly increases soil P availability and mobilizes soil micronutrients. The application of polyphosphate can be recommended as a pragmatic P management strategy in agriculture: however, soil temperature and pH should be taken into account when using polyphosphate fertilizers.     

Influence of pyrolysis temperature on biochar property and function as a heavy metal sorbent in soil

While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood?cottonseed hull≈grass≈pine needle?broiler litter. To examine how biochar properties translate into its function as a heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to the surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.     

Influence of pyrolysis temperature on chemical and physical properties of biochar from sewage sludge

The use of sewage sludge biochar (SSB) for agro-environmental purposes has been increasing. However, due to the strong influence of pyrolysis temperatures on its production, there is great variation in its final properties. In this regard, efforts to generate relationships among many correlated SSB properties may help to understand this influence. This study sought to evaluate the effect of pyrolysis temperature on agro-environmental physicochemical properties of SSB. Biochars from sewage sludge (SS) were produced at 300, 400 and 500°C and their physicochemical properties were evaluated in comparison to SS samples. The increase in pyrolysis temperature decreased C, N, and H contents and the H/C atomic ratio, while increasing the C/N ratio. The pyrolysis process increased pH values, the surface area and pore volume and enriched the SSB with macro and micronutrients. Considering all variables together, the biochar produced at 300°C was that which showed the greatest nutrients availability, such as N total, S, NO₃^?, NH₄⁺, Ca²⁺ and Mg²⁺. Conversely, SSB produced at 500°C showed higher recalcitrant organic matter and alkalinity, important properties for C sequestration and the correction of acidic soils. The combined application of SSB produced at lower and higher pyrolysis temperatures should be furthered studied.     

生物肥料磷的利用效率：生物有效性和组分

Although to date some technologies producing bio-based phosphorus (P) fertilizers have been proposed and implemented, the efficient use of the recovered products is still limited due to legislative constraints and lack of insights in the P release with time and in the corresponding mechanisms. The aim of this work was to evaluate the fertilizer performance in terms of P release and use efficiency of recovered struvite, FePO₄-sludge, digestate, and animal manure as compared to fossil reserve-based mineral triple superphosphate (TSP). First, product physicochemical characteristics and P fractions in the context of European fertilizer legislation were assessed. Next, a controlled greenhouse experiment was set up to evaluate plant reactions as well as changes of P availability in a nutrient-rich sandy soil with high P status and a nutrient-poor Rheinsand soil with low P status. Soil P fractions were determined in the extracts with water, ammonium lactate and CaCl₂, and in soil solution sampled with Rhizon soil moisture samplers. Based on all results, it is worth conducting long-term field trials to evaluate the P release effect of struvite and digestate as compared to animal manure and TSP on different soil types with varying P status. These products showed promise as sustainable substitutes for conventional P fertilizers and could contribute to a more efficient use of P in agriculture. A refined classification of P application standards/recommendations in terms of soil P status, soil texture, and fertilizer characteristics, next to the crop P demand, is recommended. Moreover, the additional use of Rhizon samplers for determination of direct available P, including dissolved organic P, is proposed for better understanding and categorization of different P fertilizers in environmental and fertilizer legislations.     

Developing an Environmental Manure Test for the Phosphorus Index

Abstract

Widespread implementation of the phosphorus (P) index has focused attention on environmental manure tests that can be used to estimate the relative availability of P in manure to runoff water. This article describes the development and use of a water extractable P (WEP) test to assess the capacity of land‐applied manure to enrich P in runoff water. WEP of surface‐applied manure has been shown to be strongly correlated to dissolved P concentrations in runoff from agricultural soils. WEP tests that have a defined water‐to‐manure‐solids ratio and involve extraction times of 30 to 120 min provide the best prediction of dissolved P in runoff across a wide range of manures. Consistent measurement of manure WEP can be achieved with manure sample storage times of up to 22 days (4°C), acidified extract holding times of 18 days, and solid separation by either centrifugation or paper filtration. Reproducibility of WEP tests is comparable to that of other common manure tests (e.g., total P), as verified by within‐laboratory and inter laboratory evaluations. A survey of 140 livestock manures revealed significant differences in mean WEP among different livestock manures, with swine greater than poultry (turkey, broiler and layer chickens) and dairy cattle greater than beef cattle. Such results support the use of WEP‐based coefficients to modify the source component of the P index.     

Effect of moisture and temperature regimes on available phosphorus in wetland rice soils

Abstract

A laboratory experiment was conducted to evaluate the effects of water and temperature regimes on availability of soil phosphorus (P). Four soil samples with variable levels of available P collected from a long‐term P frequency trial were incubated under two moisture regimes, continuous waterlogging (CWL) and alternate wetting and drying (AWD) at 20°C and 30°C temperature for 90 days. The samples were extracted with 0.5M NaHCO₃ for available P determination after incubation. Increase in temperature increased available P content and this increase was more prominent in CWL conditions. Available P in all the soils tested was higher under CWL than AWD conditions, however, the increase in available P due to CWL environment was more pronounced in soils with higher available P.     

Effect of Water Quality Parameters on the Migration of Vinyl Chloride Monomer from Unplasticized PVC Pipes

The migration of vinyl chloride monomer (VCM) from unplasticizedpolyvinyl chloride (uPVC) pipes was investigated using locallymanufactured pipes. Specimens of 33 cm long were used throughoutthe research. The investigation was carried out under differentconditions of water temperature, pH and total dissolved solidsconcentration and at different durations of exposure. The VCMconcentration in the water was evaluated using the gaschromotography (GC)/head-space technique. A VCM concentration ofmore than 2.5 ppb was detected after 30 days of exposure at45 °C. The initial VCM concentration in the uPVC pipewas predicted using equations derived from Fick's first law ofdiffusion. Water tenperature did not affect the migration ofVCM, unless it was raised to high values (i.e. 45 °C).Total dissolved solids (TDS) and pH of water were found toaffect the release of VCM from uPVC pipes. Diffusion rate of VCMwas predicted as a function of pH or TDS values.