Freeman Ntuli

Extraction and precipitation of phosphorus from sewage sludge

Raw sewage sludge from East Rand Water Care Association (ERWAT) had high phosphorus (P) content, approximately 15.2% (w/w) P2O5, which indicates a potential resource for the limiting nutrient. Leaching sewage sludge with 1M sulphuric acid at 5% solid loading for 2h resulted in an 82% phosphorus extraction. However, the phosphorus was recovered as iron phosphates, thus a further purification step using ion exchange to remove iron was required to increase the degree of P release. Magnesium oxide and ammonium hydroxide were used as magnesium and nitrogen sources, respectively, as well as pH regulators to precipitate P as struvite. 57% struvite was precipitated and the total phosphorus content of the precipitate was 25.9%. Kinetic studies showed that the leaching of phosphorus follows the Dickinson model for the first 100min with a rate of reaction of about 2×10-5s-1. The rate limiting step is controlled by diffusion. Phosphorus solubility in 2% critic acid was almost 96%, which is the amount of phosphorus available to plants if the precipitate is applied as a fertiliser. Environmental, gram-positive Bacillus subtilis were found in the precipitate, which are harmless to the environment since they already exist in the soil where the precipitate can be applied as a fertiliser.

Designing of sampling programmes for industrial effluent monitoring

IntroductionMonitoring of effluent discharges from industrial establishments discharging directly into municipality sewers is one of the major water pollution control activities conducted by municipalities. For largely industrialised municipalities, the task can be quite expensive and not effective if sampling programmes are not properly designed. In most cases, samples are randomly collected without proper knowledge of the discharge patterns of various industries. As a result, the information obtained does not give a good reflection of the quality of effluent being discharged.MethodsThese problems can be resolved by adapting a statistical approach to the design of sampling programmes. This approach is useful in determining the frequency of sampling, the number of samples needed to estimate the average concentration of target pollution indicator parameters and the magnitude of the uncertainty involved.ResultsThe benefits and applications of this approach are demonstrated by a case study presented in this paper. It was found that the number of samples and cost of sample analysis can be greatly reduced by the use of systematic instead of random sampling.ConclusionThe statistical approach greatly improves the estimate of monthly means of pollution indicator parameters and is an effective approach for pollution control when coupled with the “polluter pays principle”.

Parametric effects on leaching behavior of nickel-copper matte in ammonia

Leaching, which is described as the extraction of soluble constituents from a solid by means of a solvent, is an important separation technique in the refining of precious metals from their matte. It is, therefore, important to investigate the extraction behavior of metals from the matte, which is the focus of this study. This study reports the influence of concentration of the solvent (ammonia), leaching temperature, leaching time, and pH on the recovery of nickel and copper from the matte. The elemental composition analysis of the matte indicated that it contains 23% copper, 37% nickel and 1.1% ferrous compound. The analysis also showed that the major mineral phases present in the matte were heazlewoodite (Ni3S2), chalcocite (Cu2S), djurleite (Cu1.9S), and nickel alloy. The leaching parameters studied were concentration of ammonia (1.5, 2.0, 2.5, and 3.0 M), leaching time (0–270 min, at 15 min sampling interval), leaching temperatures (50°C, 60°C, and 70°C), and pH (9.3–11.2). The results obtained revealed that the recovery of nickel and copper from the matte was greatly influenced by the concentration of ammonia, leaching time, leaching temperature, and pH. It was established from this study that the highest dissolution of nickel and copper was obtained at 3 M and 2 M ammonia concentration, respectively. The results also revealed that a decrease in the pH of the solution resulted in a decrease in both nickel and copper recovery, with maximum leaching time of 270 min. It was observed that less than 50% of both nickel and copper was leachable due to the presence of metal alloys. The analyses of the results also showed that as the leaching temperature increased from 50°C to 60°C, the amount of nickel and copper that was recovered from the matte significantly increased. However, there was reduction in the amount of nickel and copper recovered from the matte as the temperature was increased from 60°C to 70°C, due to loss of ammonia by evaporation. The shrinking core model was used to explain the behavior of the recovery of these metals at different temperatures, and both metals were found to be favored by diffusion controlled reaction.

Temperature effect on volatile organic compounds – polydimethylsiloxane Interactions

og V ) of 13 volatile organic compounds (VOCs) of environmental importance between the gas and liquid stationary phase (polydimethysiloxane) (PDMS) were studied using the gas liquid chromatographic technique (GLC). Temperature was varied from 303.15K to 423.15K to allow transport calculations for different seasons. Four PDMS polymers with average molecular weight ranging from 760 to 13 000 were used as solvents. The results of this work confirm that PDMS is well suited for VOCs scrubbing from waste gas streams. Linear plots of log g V against T 1 were obtained in all cases permitting predictions and interpolations to temperatures not studied here. Also dependable enthalpies and entropies of solute transfer from the mobile phase to the stationary phase can be calculated. The specific retention volumes reported in this work are in agreement with literature for similar systems. Efforts were taken to ensure the best possible accuracy and trace the possible sources of error. A gas liquid chromatographic system which secured a simple retention mechanism and showed reproducible solute retention over a long period of time was devised.

Torrefaction of landfill food waste for possible application in biomass co-firing

Greenhouse gas emissions and municipal solid waste management have presented challenges globally. This study aims to produce a high-quality biochar with properties close to bituminous coal from landfill food waste (FW). FW was analyzed by proximate and ultimate analyses to determine its fuel properties and elemental composition before torrefaction. Temperature was varied from 200 to 300 °C at a constant residence time of 40 min and 10 °C/min heating rate. Calorific value, mass yield, energy yield and energy density were computed and used to determine the quality of the resulting biochar. Quality of raw food waste was also determined by elemental analysis. Thermal evolution was then investigated using hyphenated Thermogravimetric Analysis (TGA) and Fourier Transform Infra-Red Spectrometry (FTIR). Torrefaction was done at 225 °C, 275 °C and 300 °C. The calorific value was upgraded from 19.76 MJ/kg for dried raw food waste to 26.15 MJ/kg for torrefied food waste at the appropriate conditions which were 275 °C, 40 min and 10 °C/min. The higher heating value was comparable to that of bituminous coal from Anglo Mafube in South Africa. Elemental analysis of biochar showed an increase in carbon content with temperature due to loss of oxygen containing volatiles. This agreed with TG curves and FTIR spectra which confirmed release of H2O, CO and CO2. This resulted in a more hydrophobic solid fuel with high energy density. Food waste can therefore be upgraded to a biochar with similar fuel properties as pulverized coal used in coal fired boilers.

Effect of attapulgite calcination on heavy metal adsorption from acid mine drainage

Attapulgite calcined at 973.15K was characterized and utilized as an adsorbent for the removal of heavy metals and neutralization of acid mine drainage (AMD) from a gold mine. Batch adsorption experiments were carried out using a thermostatic shaker. Activated attapulgite showed that it can neutralize AMD as it raised the pH from 2.6 to 7.3 after a residence time of 2 h. Metal ion removal after 2 h was 100% for Cu (II), 99.46% for Fe (II), 96.20% for Co (II), 86.92% for Ni (II) and 71.52% for Mn (II) using a 2.5% w/v activated attapulgite loading. The adsorption best fit the Langmuir isotherm; however, Cu (II), Co (II), and Fe (II) data fit the Freundlich isotherm as well. Calcination at 973.15 K resulted in the reduction of the equilibrium residence time from 4 to 2 h, solid loading reduction from 10 to 2.5% m/v and an increase in maximum adsorption capacity compared with unactivated attapulgite.

Potassium Aluminate Geopolymerisation of Acidic Gold Mine Tailings

Acidic gold mine tailings were alkaline activated using KOH. The effect of potassium aluminate (KA) on the strength and durability of the geopolymers was investigated. A 2.8 KA:KOH geopolymer had a UCS of 18.10 MPa after curing for 5 days at 100 °C. There was an increase in UCS with an increase in loading of KA up to a ratio of 2.8. Beyond the KA:KOH ratio of 2.8, there was a 48% drop in UCS due to excess K+ ions in the system which resulted in the loss of charge balance of the system leading to reduction of UCS. It is worth mentioning that the KA:KOH ratio of 2.8 represented a Si/Al ratio of 1.02. This study showed that KA activation of acidic gold mine tailings is an attractive route to stabilise/solidify hazardous tailing material. Though there is use of elevated temperature to achieve high strength for the KA based geopolymer, this pales in comparison to energy requirements of cement manufacturing and clay brick firing.

Municipal solid waste generation and characterization in the City of Johannesburg: A pathway for the implementation of zero waste

The huge increase generation of municipal solid waste (MSW) has recently become an issue of global concern. This is because waste generation increases as the population increases and the management of this waste has equally become a bit difficult. This study aims at determining the characterization and the pattern of municipal solid waste (MSW) in the City of Johannesburg (CoJ), South Africa. The results revealed that plastics and organic wastes constitute the highest waste content in both the daily refuse (DR) and round collected refuse (RCR). The results further showed that DRs are 28% and 26% for plastic wastes, while 28% and 29% organic wastes accounted for the RCRs during the summer and winter seasons respectively. The carbon to nitrogen ratio (C:N) content of the food wastes employed in this study was evaluated to be 22.66 and the empirical equation generated was C27H44NO16. STATA 12 software and ANOVA statistical technique were used to evaluate the seasonal variation between the winter and summer seasons (spanning a space of six months). The p-values obtained for the DR was (p-value = 0.9775) and for the RCR, it was (p-value = 0.9760) at 95% confidence level using STATA 12 tests. Similarly, the p-value obtained for the DR was (p-value = 0.999) and for the RCR, it was (p-value = 0.991) in turn using ANOVA tests at 95% confidence level. Furthermore, Minitab software was used to forecast the trend of waste generation between 2016 and 2025. Based on the overall results, it was concluded that the differences between the wastes generated in both seasons were not statistically significant (p > 0.05). Furthermore, a total of 102,406 tonnes of wastes would be generated during the period under consideration (a period of ten years). This indicates a negative trend for CoJ in terms of waste generation. However, this trend can be mitigated through Zero waste (ZW) implementation.

Geotechnical Properties and Microstructure of Lime-Fly Ash-Phosphogypsum-Stabilized Soil

The use of industrial waste as a potential stabilizer of marginal construction materials is cost effective. Phosphogypsum and fly ash are industrial wastes generated in very large quantities and readily available in South Africa. In order to explore the potential stabilization of vastly abundant expansive soil using larger quantity phosphogypsum waste as a potential modifier, composites with a mixture of lime-fly ash-phosphogypsum-basic oxygen furnace slag were developed. However because of the presence of radionuclide, it was necessary to treat the phosphogypsum waste with mild citric acid. The effect of the acid treatment on the geotechnical properties and microstructure of expansive soil stabilized with phosphogypsum-lime-fly ash-basic oxygen furnace slag (PG-LFA-BOF) paste was evaluated, in comparison with the untreated phosphogypsum. Expansive soil stabilized with acid-treated PG-LFA-BOF paste exhibited better geotechnical properties; in particular, the high strength mobilized was associated primarily with the formation of various calcium magnesium silicide and coating by calcium silicate hydrate and calcium aluminate hydrate. The soil microstructure was improved due to the formation of hydration products. The stabilized expansive soil met the specification for road subgrades and subbase. Stabilization of expansive soils with phosphogypsum, fly ash, and basic oxygen fly ash does not only improve engineering properties of soil but also provides a solution in relation to disposal and environmental pollution challenges.

Investigation of Cu (II) Removal from Synthetic Solution by Ion Exchange Using South African Clinoptilolite

The objective of this study was to investigate the effect of NaCl, KCl and acid (HCl), on South Africa clinoptilolite used as an adsorbent in the ion-exchange process for the removal of cations (Cu II) from wastewater. The kinetic parameters such as ∆H, ∆S and ∆G affecting the adsorption of Cu (II) ions were studied. The adsorption of Cu (II) from synthetic waste water was found to be dependent on pH, temperature, contact time and initial adsorbate concentration. The pH was varied from 2.5–6 and the optimum pH for Cu (II) removal was found to be 4.0. The removal of Cu (II) ions increased with time and attained saturation in about 60–70 min. The equilibrium data showed that the adsorption was endothermic in nature. Kinetics data showed that at higher temperatures, the rate of adsorption is higher for the clinoptilolite in natural zeolite and that Langmuir equation successfully described the adsorption process.