abstract: In situ remediation of contaminated aquifers, specifically in situ bioremediation (ISB), has gained popularity over pump-and-treat operations. It represents a more sustainable approach that can also achieve complete mineralization of contaminants in the subsurface. However, the subsurface reality is very complex, characterized by hydrodynamic groundwater movement, geological heterogeneity, and mass-transfer phenomena governing contaminant transport and bioavailability. These phenomena cannot be properly studied using commonly conducted laboratory batch microcosms lacking realistic representation of the processes named above. Instead, relevant processes are better understood by using flow-through systems (sediment columns). However, flow-through column studies are typically conducted without replicates. Due to additional sources of variability (e.g., flow rate variation between columns and over time), column studies are expected to be less reproducible than simple batch microcosms. This was assessed through a comprehensive statistical analysis of results from multiple batch and column studies. Anaerobic microbial biotransformations of trichloroethene and of perchlorate were chosen as case studies. Results revealed that no statistically significant differences were found between reproducibility of batch and column studies. It has further been recognized that laboratory studies cannot accurately reproduce many phenomena encountered in the field. To overcome this limitation, a down-hole diagnostic device (in situ microcosm array - ISMA) was developed, that enables the autonomous operation of replicate flow-through sediment columns in a realistic aquifer setting. Computer-aided design (CAD), rapid prototyping, and computer numerical control (CNC) machining were used to create a tubular device enabling practitioners to conduct conventional sediment column studies in situ. A case study where two remediation strategies, monitored natural attenuation and bioaugmentation with concomitant biostimulation, were evaluated in the laboratory and in situ at a perchlorate-contaminated site. Findings demonstrate the feasibility of evaluating anaerobic bioremediation in a moderately aerobic aquifer. They further highlight the possibility of mimicking in situ remediation strategies on the small-scale in situ. The ISMA is the first device offering autonomous in situ operation of conventional flow-through sediment microcosms and producing statistically significant data through the use of multiple replicates. With its sustainable approach to treatability testing and data gathering, the ISMA represents a versatile addition to the toolbox of scientists and engineers. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2013

Potato (Solanum tuberosum L.) is one of the most important tuber crops globally and is classified amongst the most crucial food crops in Africa. South Africa has a very vibrant potato industry, producing about 2.5 million tonnes every year, with quantities bettered only by Algeria and Egypt. Potato production is very expensive (R150 000 ha-1), with fertilizers contributing 20%. Potato is highly reliant on steady nutrient supply and any deficiencies result in poor yield. Potato fertilizer demand is higher than that of other crops such as cereals and it has a very unique demand for phosphorus (P), which is vital from its early development to maturity. In addition, potato has a very shallow root system, which compromises P uptake, making most potato cultivars ineffective in nutrient uptake. Therefore, high P fertilizer rates are applied of which <20% is utilized by plants within a few days after application and about a further 4% within the next 10 days, mostly due to fixation. The production of P fertilizer, such as super phosphate (SP) is energy-consuming, costly and emits fluorine. There is also a risk of cadmium (Cd) accumulation in soils and plants due to the heavy fertilisation, posing a risk to human health, animals and aquatic life. Runoff phosphorus leads to eutrophication of water bodies. In addition, P fertilizer production is severely threatened by declining rock phosphate (RP) reserves, expected to hit a low by 2200. This will result in a hike in P fertiliser prices as miners move to low concentration ores. The high demand of P in potato, the environmental and human health risks, the high costs and declining reserves, all call for prudent and sustainable management of P in potato production. Nitrate and ammonium results in contrasting plant metabolism and growth. Most importantly through rhizosphere modification where ammonium supply results in reduced soil pH while nitrate results in increased soil pH. The pH reduction in ammonium supplied soils increases P dissolution and availability while the opposite is noted in nitrate. Most of the studies in this phosphorus-nitrogen interaction have been conducted on tree species, grasses and cereal crops with little done on tuber crops. In addition, the application of RP directly to plants could help cut the emissions, processing costs and environmental contamination associated with chemical P fertiliser production. There is, therefore, an urgent need to develop P fertilizer management systems to effectively manage this finite resource by improving its use efficiency for maximum yield at optimum application rates. To attain this objective, two experiments were conducted, namely a laboratory study to investigate the interaction between nitrogen forms and phosphorus sources in soil columns without a test crop, and a glasshouse pot trial to investigate the same interaction with potato as test crop. The column study treatments comprised of two soil types, N supplied as ammonium or nitrate and three P sources (SP, RP and a P0) to give 12 treatments that were replicated four times to give 48 columns. Mechanical dry packing method was used. The columns were leached with one pore volume over four watering events (1, 21, 42 and 63 days) and terminated on day 90. The leachate was collected in glass bottles at the column bases and analysed for pH, phosphorus, calcium, potassium and magnesium contents. A glasshouse pot trial was set up at the University of Pretoria Experimental Farm with potato cultivar Mondial as the test crop over two seasons, with a high and low initial soil P in season one and two, respectively. One minituber was planted per 10 litre pot. Watering was done using a pressure compensated drip irrigation system. Data was collected at tuber initiation (TI) and at the end of the season (ES). Parameters assessed included plant height, dry masses, number of tubers initiated, yield, leaf tissue and soil P status. Significant phosphorus-nitrogen interactions occurred on most assessed parameters in both trials. The exceptions were pH, potassium, phosphorus, calcium and magnesium levels, at some stages of the column study. Significant phosphorus-nitrogen interactions were noted at all watering events for both soil and leachate pH, phosphorus, potassium, calcium and magnesium concentration. In the pot trial, significant phosphorus-nitrogen interactions were noted for most of the plant measurements at both the TI and ES assessment periods with a few exceptions. Ammonium + SP produced the highest tuber initiation rate and final yield, as well as highest tissue and plant available P levels in both seasons. In the leachate and soils at the end of the column study, as well as at both stages assessed in the pot trial, ammonium treatments tended to have higher P contents. In the pot trial, ammonium treatments gave taller plants, but with lower dry mass compared to nitrate. Nitrate treatments had higher soil and leachate pH compared to ammonium treatments in both trials. Plants supplied with SP tended to have longer haulms and roots, higher haulm and root biomass and higher yield compared to treatments with RP and P0. The findings of these trials indicated that ammonium results in higher phosphorus dissolution (with or without a crop) and uptake by plants due to increased soil acidity. The resulting effect on potato crop is an increase in the number of tubers initiated and higher yields. However, the positive effect of ammonium was mostly achieved in combination with superphosphate. Rock phosphate, despite the increased yields, compared to treatments without P, gave inferior plant performance and is therefore not a worthy substitute for superphosphate. / Dissertation (MSc (Agric))--University of Pretoria, 2020. / Plant Production and Soil Science / MSc (Agric) / Unrestricted

Major impacts of current and pre-regulatory mining activities on the environment include the generation of acid mine drainage (AMD) and metal(loid)-laden acid sulfate soils. Current remediation techniques are mostly cost prohibitive due to high energy, material, and labor requirement. This study investigated two complementary low-cost methods that harnessed the metal(loid)-removing and acid-neutralizing properties of drinking water treatment residuals (WTRs) and the uptake (phytoremediation) potential of vetiver (Vetiviera zizanioides L.) and pokeweed (Phytolacca americana L.) to attenuate and immobilize metal(loid)s from natural AMD and metal(loid)-contaminated soil. Metals were removed from AMD by using a reverse flow fluidized column filter and hydroponic phytoremediation with vetiver and pokeweed. Metals were immobilized in soil through the amendment with Fe and Ca-WTR complimented by the uptake and translocation of metals by vetiver and pokeweed. Experiments were performed under controlled greenhouse conditions as well as under natural Illinois environment in simulated field conditions. Furthermore, the integrated effects of WTR application and the growth of vetiver on soil erosion were also studied. Physicochemical analysis of AMD and soil samples from the Tab-Simco abandoned mine in the Illinois Coal Basin, U.S.A, showed significant concentrations of major metals and metalloids such as Fe, Al, Mn, Zn, Ni, Cu and As at acidic pH levels. The degree of soil contamination at the site was spatially variable with respect to the location of the main AMD seep. Physical, chemical, agronomic and mineralogical characterization of locally acquired water treatment residuals (WTR) showed that the silty and alkaline (pH ≈ 7.0-9.1) materials also contained significant amounts of plant required micronutrients. The presence of amorphous phases of mostly metal (oxy)hydroxides, alkalinity, and porosity of the WTRs suggested the potential to neutralize acidity and capability to remove metal(loid)s in contaminated soils and AMD. Recorded metal removal (%MR) rate by WTR was rapid in the first 80 min in a batch agitation study, except for Mn. Thus, high metal removal ranging from 99.8% to 84.9% at selectivity sequence of Al>Fe>Cu>Zn and Mn (9.6%) was obtained at equilibrium. The pH of the AMD was also increased from 2.6 to 6.7. Analysis of leachate samples from gravity-drained columns following simulated rain events in a greenhouse study showed reduced concentrations of Al, Fe, Mn, Zn, Cu, As and Pb at sustained neutral pH compared with unamended control columns during the 12 weeks study period. Metal immobilization in soil by the lower amendment rates of WTR was comparable to the higher application rates and also showed lower oxalate extractability of metals. Tissue analysis of pokeweed and vetiver hyperaccumulators showed appreciable uptake of relevant elements although translocation was relatively low in both. The analytical results at the greenhouse scale was reproducible in a simulated field scale study under natural Illinois environmental condition where the best amendment rate including 50 g/kg Fe-WTR and 15 g/kg of Ca-WTR and manure helped to improve metal(loid) retention, soil structure and enhanced vetiver growth which subsequently aided in reducing the rate of erosion to levels comparable to bermudagrass which was used as control. The developed integrated WTR fluidized column and phytoremediation technique with vetiver and pokeweed under hydroponic conditions sequentially removed significant quantities of most heavy metals from AMD. Thus, the overall findings showed that the locally collected WTRs - the otherwise waste materials, showed high metal-removing and acidity-reducing capabilities in AMD and contaminated soil treatment applications. The similarity between the results obtained from the laboratory and simulated field study also showed that laboratory/greenhouse experiments may serve as reliable proxies for field responses in applications such as soil and water conservation in agricultural environments, remediation of abandoned mine lands, as well as wastewater treatment systems.