No description available.

No description available.

No description available.

Sewage sludge is a potentially valuable resource that can enhance both the structure and fertility of soil. However, it can also harbour enteric pathogens which pose a significant socio-economic risk to society. Therefore it is important to understand the factors that govern the persistence of such pathogens in soil, when co-introduced with sewage sludge, in order to mitigate risk and to further avail of such a valuable resource. This research aimed to clarify how microbial activity and the presence of sewage sludge would influence the persistence of co-introduced enteric pathogens in soil. It was theorised that the addition of sewage sludge to soil would cause the formation of organic matter (OM) and nutrient-rich niches. Such niches, in turn, would encourage the enhanced activity of the local soil microbial community, instigating greater competition for local resources, i.e. a hot spot of microbial activity that would lead to a decline in the introduced enteric pathogens. It was also hypothesised that the interface between the soil and sewage sludge may influence such interactions, as the physicochemical characteristics could affect the extent of exposure and subsequent interactions between enteric pathogens and the soil microbial community. These theories were investigated using four different perspectives that linked closely with each other. In initial studies, two cohorts of microcosms consisting of different proportions of sewage sludge to soil were inoculated with either E. coli or S. Dublin and destructively sampled over a 42 day period. E. coli prevailed at greater numbers when inoculated directly into soil and sewage sludge, whilst it declined to the greatest extent within mixed microcosms containing 25% sludge. All treatments containing S. Dublin appeared to decline at a similar rate, which was more linear than the decline observed within treatments inoculated with E. coli. From these findings, it can be concluded that there are no direct relationships between the proportion of sludge to soil and its affect on pathogen survival. A subsequent experiment implemented a similar treatment strategy, whilst using indigenous sewage sludge E. coli. The use of this microbe provided data which was more suited to the original premise of this work, as under such scenarios it would be indigenous sewage sludge E. coli that would be of concern. Therefore, microcosms consisting of different proportions of sewage sludge, containing indigenous E. coli, were destructively sampled over a 56 day period. The indigenous sewage sludge E. coli exhibited a more consistent linear decline after the first week. However, the indigenous E. coli were again not significantly affected by different proportions of sewage sludge to soil. It was theorised that this lack of variation in response to varying proportions of sewage sludge to soil may have been associated with a lack of available substrate within the system, or some form of partitioning effect between soil and sewage sludge matrices, which prevented the microbial communities from interacting. To further develop these concepts, the effect of two contrasting substrate amendments and their location (either sewage sludge, soil or within both matrices) was also investigated in relation to the persistence of sewage sludge-derived E. coli. Microcosms consisting of both pure samples and mixtures of sewage sludge or soil were inoculated with sewage sludge-derived E. coli and destructively sampled over a 42 day period. Respired CO2 and microbial carbon were also quantified. The addition of a simple substrate, glucose, instigated a peak in microbial respiration and accelerated the decline of sewage sludge-derived E. coli and also marginally increased the microbial biomass. This is similar to the original concept proposing that a hot spot of microbial activity could instigate pathogen die-off. In contrast, amendment with a more complex substrate, yeast extract, had little effect on the decline of sewage sludge-derived E. coli. Nor did respiration increase immediately after amendment. There was also no observable partitioning effects between soil or sewage sludge with either amendment. This suggests that a lack of available substrate could influence microbial dynamics and thus the decline of E. coli. To further explore this phenomenon the repeated addition of glucose and its effect on the survival of sewage sludge-derived E. coli was investigated. It aimed to highlight the impact of sustained competition for resources on persistence, whilst mimicking the recurrent input of carbon that occurs in plant/soil systems. Microcosms consisting of both pure and mixtures of sewage sludge or soil were inoculated with sewage sludge-derived E. coli and destructively sampled over a period of 105 days. Respired CO2 and microbial carbon were again analysed. It was found that the repeated addition of glucose did not cause a significant decline in the survival of sewage sludge-derived E. coli. Notably, some small increases in E. coli numbers were observed after the second and third amendments of glucose. Overall, these findings suggest that hot spots of activity can instigate a decline in enteric pathogens, though such interactions are dependent upon the availability and quantity of nutrients and organic carbon within the matrices. These findings could aid in developing the use of amendments in sewage sludge that would minimise the survival of enteric pathogens in soil. They also provide a framework which pinpoints the factors that should be considered when investigating the persistence of enteric pathogens in the soil environment. Such amendments and knowledge pertaining to the key factors in the survival of enteric pathogens could further decrease the social and economic risk which the use of sewage sludge poses when used in agricultural systems.

No description available.

Egypts population was projected to increase from 20 million in the 1960s to 67 million by 2000. With this increase in the population, an increase in food production of 200% to 300% is become necessary to meet food demands. In addition to the increasing demand for food, the population increase will result in increased amounts of human wastes. This will, in tum, need to be disposed of in ways other than the traditional dumping in the nearest stream or the Nile River. It is therefore vitally important to utilize as much as possible of this human waste (biosolids) as an organic fertilizer and soil conditioner to increase sandy soil productivity in Egypt. Composting is recognized as a cost-effective environmentally sound process for treatment of biosolids, even though they may contain substances, which pose potential hazard to the environment or food chain. The aim of this study was therefore set out to develop a management strategy that used biosolids compost as a soil conditioner and fertilizer to increase their agronomic benefits and minimize their environmental impacts when applied to newly reclaimed sandy soil. The agronomic benefits and the environmental impacts of applying biosolids compost to sandy soil were identified through a series of glasshouse, pot, and incubation trials using tomatoes and grass crop. Tomato was chosen as it represents a vegetable with a high potential for heavy metals uptake and because of its world-wide important as vegetable crop. The results of this work showed that, compost application had the capacity to stimulate vigorous growth, nutritional status, production levels of tomato plants, 'and to increase N recovery by tomato plants compared to control. The major nutrient concentrations of N, P, and K in tomato leaves taken from plants grown on compost. The stem radius of tomato plants grown on the compost amended-plots were about twofold thicker in the case of the highest compost application rate (360 t/ha) than the plants from control plots. At 360 t/ha application rate, the tomatoes production level response for the compost-treated plots was 13.3 kg/plot while it was 1.8 kg/plot for the control. This represents an increase of more than 700% over the control plots. Nitrogen recovered by tomato crop following compost addition exceeded 20% of the total applied N after one and two compost applications. All these improvements in growth quality parameters of tomato plants were not significantly different at the higher compost application rates of 240 and 360 t/ha. This finding indicates that the plant response due to the increasing of compost application rate is subject to diminishing returns. The incorporation of biosolids compost into sandy soil has established sufficient grass covering area and improved soil aggregate stability compared to mulched-applied compost. The range in grass covering was a low of 7.9% for the control to 100% for incorporated applied compost at all application rates. The grass covering ranged from 7.9% for the control to 70% for mulched applied compost at the highest application rate. Incorporated-applied compost had more large aggregates and less small aggregates and consequently the overall aggregate stability ranged from 25 to 30% compared to 6 to 11% in the case of mulched-applied compost. The superiority of the incorporated-applied compost to the mulched-applied compost on aggregate stability was due to the stabilizing effects of the organic matter. The N mineralization rate has suggested that rapid and extensive N accumulated in the soil solution soon (60 days) after compost addition and the amount of N recovered was in excess of 20% of the total applied N. This value is higher than the 10% value reported elsewhere in the literature. Soil analysis of the compost treated plots revealed significant increases in soil pH, organic matter, CEC, soluble salts, and total heavy metals compared to control. Major considerations in recycling of biosolids compost on newly reclaimed sandy soils are the increase in soluble salts, the groundwater contamination by nitrate. The increase in soluble salts following compost addition was at a level that could reduce yields in sensitive crops. High application rates of compost at high moisture status resulted in high levels of nitrate in the soil solution (> 50 mg/l). Another concern was the increased amounts of heavy metal accumulation in the soil profile where more than 90% of the compost- applied heavy metals were present in the top 20 cm of soil plots, but these increased amounts were still far below the plant toxicity levels. The results of this study clearly indicated that incorporated biosolids compost does increased agronomic benefits and does not pose the same environmental problems as mulched biosolids compost when used as a fertilizer with large-scale application rate. Application of biosolids compost significantly increased the concentration of heavy metals in tomato fruit compared to control. Crop recovery of compost-applied Zn and Cu by tomato plants was less than 0.5% at all compost application rates regardless of the method of application, and was significantly greater by tomato plants grown on compost-mulched plots than incorporated. Crop recovery of compost-applied Ni, Pb, Cd, and Cr by tomato plants was less than 0.08% at all compost application rates. In general, no health problems could be foreseen to humans or animals from food chain movement of these negligible amounts of heavy metals. With regard to heavy metal concentrations in the soil leachate, the data gave wide assurance that the environment is successfully protected. From this study, it could be concluded that high loading rates of good quality compost to sandy soils is ergonomically valuable with limited potential environmental risk if managed properly. Under the conditions of this study, incorporation of biosolids compost into sandy soil using drip irrigation system was the best management strategy practice to reach optimum agronomic benefits while minimizing environmental impacts.

No description available.

No description available.

A review of the literature was made on composting and the effects of non-composted and composted materials on soil properties and plant growth. A comparison of the effects of three levels of straw and composted straw on the rate of mineralization of carbon from a soil over 311 days was made. In another experiment the rate of carbon mineralization from straw and compost added to a soil adjusted to four different pH levels and maintained at three different moisture levels, including waterlogging, was studied over 118 days. A comparison was made of the effects of uncomposted straw plus mineral nitrogen, composts prepared from straw with three different accelerators (nitrochalk, sewage sludge and dried blood), a grass compost, and mineral nitrogen alone on the performance of ryegrass and the uptake of nitrogen, phosphorus, potassium, and magnesium in pot tests using a soil of three different pH levels. The performance of ryegrass and uptake of major nutrients was studied in soil (at three pH levers) treated with three levels each of straw and straw composted with dried blood. A study was made of the effects of straw and four different composts on the performance of ryegrass in pot tests with a calcareous soil with either nitrogen or phosphorus as the only limiting nutrient. The residual effects of straw and four different composts were studied in a pot test by growing two successive crops of wheat. The availability of nitrogen from four straw composts, prepared with different accelerators, and containing very similar levels of total nitrogen was studied in a sand culture test and compared with the amount of nitrogen mineralized in an incubation test.

Livestock slurry is a valuable source of phosphorus (P) fertiliser for crops, but can also result in eutrophication following mobilisation and delivery to watercourses. The transfer of slurry-derived P to watercourses is likely to be strongly influenced by its particle size distribution and the chemical form of the P within the slurry. Advanced slurry processing (e.g. acidification, anaerobic digestion) is also likely to alter the forms and distribution of P within slurry particle size fractions. In response to this, this thesis explores the effects of slurry processing on P speciation within a range of slurry particle size fractions and on potential P bioavailability and movement through soil. The P characteristics of cattle slurry, acidified slurry, anaerobically digested slurry, in terms of P speciation of different particle size fractions, was studied in Chapter 3-5. The results showed that in the whole untreated cattle slurry, labile inorganic P (IP-H2O + IP-NaHCO3) and labile organic P (OP-H2O + OP-NaHCO3) dominated the total P (TP) of the whole slurry (45% and 24% of TP respectively). Acidification increased the labile inorganic P proportion to 55% of TP and decreased the stable P (IP-HCl + OP-HCl + TP-Residue) proportion from 21% to 15% of the TP of whole slurry. Anaerobic digestion increased the labile inorganic P and moderately labile P (IP-NaOH + OP-NaOH) proportions of whole slurry to 53% and 12%, but decreased the labile organic P proportion to 12% of TP. After physical separation, the proportion of TP in the liquid fractions (< 2000, < 500, < 63 μm) represented by labile inorganic P were greater than that of the solid fractions (> 2000, > 500, > 63 μm), while solid fractions tended to show greater proportions of moderately labile and stable P than liquid fractions. After acidification, the P speciation of the solid fractions showed little change. However, the labile inorganic P and the moderately labile P proportions increased in TP in the acidified liquid fractions, while stable P proportion in the liquid fractions decreased. After anaerobic digestion, in the TP of both solid and liquid fractions, the labile inorganic P and moderately labile P proportions increased, while the labile organic P proportion was reduced. The colloidal fraction (0.45-63 μm) accounted for 62% of the TP of whole untreated cattle slurry. Acidification reduced this proportion, while anaerobic digestion did not change it. In contrast, anaerobic digestion increased the labile inorganic P content of the colloids. P availability in soil after slurry application was explored in an incubation experiment monitored by sequential fractionation method (Chapter 7), and in a pot experiment involving P uptake by ryegrass (Chapter 8). The vertical mobility of P in soil was studied in laboratory microcosms (Chapter 6) and a pot experiment (Chapter 8). The results showed that untreated and treated cattle slurry increased the labile P content of soil and the P lability decreased gradually over time. Ryegrass P uptake was also increased by addition of different slurries. However, the differences between untreated and treated slurry amended treatments was not necessarily significant for labile P content in the soil and P uptake by ryegrass. In Chapter 6, the results implied that colloid-associated P in cattle slurry caused greater potential P leaching and that anaerobic digestion even increased this mode of P loss. Although in the pot experiment, slurry amended treatments showed no difference in cumulative P leaching compared to the control, the colloidal fraction in untreated and treated slurries was still a dominant fraction associated with a large portion of P. Further work is necessary to demonstrate the effect of slurry processing on P bioavailability and mobility at the plot- and field-scale, and on recovering colloidal P prior to land spreading.