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Beneficiation of waste fly ash and phosphogypsum and the development of a new material

- Mashifana, Tebogo, Okonta, Felix, Ntuli, Freeman

Performance prediction of trace metals and cod in wastewater treatment using artificial neural network.

- Matheri, Anthony Njuguna, Ntuli, Freeman, Ngila, Jane Catherine, Seodigeng, Tumisang, Zvinowanda, Caliphs

Sludge to energy recovery dosed with selected trace metals additives in anaerobic digestion processes

- Matheri, Anthony Njuguna, Ntuli, Freeman, Ngila, Jane Catherine

  • Authors: Matheri, Anthony Njuguna , Ntuli, Freeman , Ngila, Jane Catherine
  • Date: 2020
  • Subjects: Additive , Anaerobic digestion , Biomethane
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/460010 , uj:40920 , Citation: Matheri, A.N., Ntuli, F. & Ngila, J.C. 2020. Sludge to energy recovery dosed with selected trace metals additives in anaerobic digestion processes.
  • Description: Abstract: The energy demand is ever rising with population increase and technology evolution. Coal consumption in South Africa is estimated to be 86% of the total energy demand. It has a high magnitude of environmental pollution and contributes to climate change. This calls for cleaner, reliable, sustainable, decarbonized, decentralized, affordable, digitized with the diversification of energy mix. The study aimed at investigating the impact of dosing selected trace metals (Ni, Co, Cu) as an additive to the substrate in the sludge to energy recovery using anaerobic processes. Sewage sludge and cellulose were used as a substrate. The biomethane potential study was carried from a 500 ml batch automated bio-digester at a mesophilic temperature of 37oC and a substratum-to-inoculum ratio (2:1) of the organic load rate. The dosed micro-nutrients acted as microbial-agents responsible for the anaerobic digestion of the feedstock. Cellulose and sludge at 0.25 mg/L (Ni) recorded the highest production of the biomethane. Cellulose inoculated with cobalt had better biomethane production at 0.02 mg/L until 0.05 mg/L. High production of biomethane was observed at the substrate with a copper concentration of 4.5 mg/L. Adding trace metals to microbial cell surroundings stimulated microbial activity and prevented the accumulation of the fatty acids. However, high concentrations beyond threshold resulted in inhibition, toxicity to the microbial-growth, which was reflected in the reduction of the production of biomethane.
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Development and size distribution of polystyrene/ZnO nanofillers

- Ayeleru, Olusola Olaitan, Dlova, Sisanda, Ntuli, Freeman, Kupolati, Williams Kehinde, Olubambi, Peter Apata

Effect of curing temperature and particle size distribution on unconfined compressive strength of raw and treated fly ash-lime modified phosphogypsum waste

- Mashifana, Tebogo, Okonta, Felix, Ntuli, Freeman

  • Authors: Mashifana, Tebogo , Okonta, Felix , Ntuli, Freeman
  • Date: 2019
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/402509 , uj:33686 , Citation: Mashifana, T., Okonta, F. & Ntuli, F. 2019. Effect of curing temperature and particle size distribution on unconfined compressive strength of raw and treated fly ash-lime modified phosphogypsum waste.
  • Description: Abstract: Voluminous quantity of phosphogypsum waste is generated by phosphoric acid manufacturing industry. Due to limited technologies available to treat the waste and render it useful, this waste is either landfilled or discharged into the sea in a form of slurry. It is critical that the focus shifts from landfilling or disposal into the sea as this result into environment contamination. This study was carried out to determine applications for raw and treated waste phosphogypsum in building and construction and determine the best conditions to produce the final product. Two significant, readily available waste materials namely phosphogypsum and fly ash were used and blended with hydrated lime. Conditions that yielded best strength from a mixture of phosphogypsum-lime-fly ash specimens were at elevated temperatures. The strengths obtained at the temperature of 80 0C were above the permissible strength for building masonry bricks of 3.5 MPa with unconfined compressive strength up to 4.8 MPa. At lower temperature of 40 0C the optimum strength obtained was at the minimal phosphogypsum content of 30%. The optimum strength was achieved at the PG content of 50% for raw PG and 60% for treated phosphogypsum at elevated temperatures. The strengths obtained for the treated phosphogypsum were lower than the minimum permissible load bearing strength due to the non-uniform particles distribution and the presence of impurities and forces of adhesion between citric acid and phosphogypsum. Increasing the curing temperature also reduced the radionuclides initially present in the raw PG without any prior treatment.
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Optical properties of bimetallic (SrO-K2O) nanofillers

- Ayeleru, Olusola Olaitan, Dlova, Sisanda, Ntuli, Freeman, Kupolati, Williams Kehinde, Olubambi, Peter Apata

  • Authors: Ayeleru, Olusola Olaitan , Dlova, Sisanda , Ntuli, Freeman , Kupolati, Williams Kehinde , Olubambi, Peter Apata
  • Date: 2019
  • Subjects: Bimetallic, nanofillers, K2O
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/396163 , uj:32881 , 2351-9789 (online) , Citation : Ayelerua, O.O. et al. 2019. Optical properties of bimetallic (SrO-K2O) nanofillers , https://creativecommons.org/licenses/by-nc-nd/4.0/
  • Description: Abstract : In this study, bimetallic nanofiller capable of usage as reinforcement was synthesized from expanded polystyrene (EPS). Bimetallic materials consist of two different metals. The bimetallic nanofiller consisting of SrO and K2O was successfully developed by the hydrothermal method which many researchers have well utilized to prepare nanoparticles in recent times. This study aims to synthesize and characterize bimetallic SrO-K2O, nanofillers from recycled expanded polystyrene (EPS). Products obtained were characterized by Zeta potential and Raman spectra. The Zeta potential was used to determine the surface charge of the nanofillers in solution. The Raman spectroscopy was used to determine the crystalline structure of the nanofillers. Based on the results, it was concluded that stability of nanoparticle materials in acidic medium decreases as the pH increases, and for the basic medium, stability reduces with decrease pH. The mixture of SrO and K2O to form SrO-K2O bimetallic oxide affects the stability of the nanofillers produced both in the acidic and basic medium. The Raman spectra indicated the Dband and Gband of the synthesized SrO, K2O and bimetallic SrO-K2O at 1006, 1008 and 1004 cm-1 and 1598, 1610 and 1606 cm-1 respectively. It was concluded that the shift in band gaps were because of structural changes in the molecules of the recycled expanded polystyrene.
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Synthesis and characterization of Sno2 nanofiller from recycled expanded polystyrene

- Ayeleru, Olusola Olaitan, Dlova, Sisanda, Ntuli, Freeman, Kupolati, Williams Kehinde, Olubambi, Peter Apata

  • Authors: Ayeleru, Olusola Olaitan , Dlova, Sisanda , Ntuli, Freeman , Kupolati, Williams Kehinde , Olubambi, Peter Apata
  • Date: 2019
  • Subjects: Environment, Nanofillers, Polymer wastes
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/395311 , uj:32772 , 2351-9789 (online) , https://doi.org/10.1016/j.promfg.2019.02.089
  • Description: Abstract : Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization’s profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s value. The trade-off capacity maximization vs operational efficiency is highlighted
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Leaching kinetics on the removal of phosphorus from waste phosphogypsum by application of shrinking core model

- Mashifana, Tebogo, Ntuli, Freeman, Okonta, Felix

  • Authors: Mashifana, Tebogo , Ntuli, Freeman , Okonta, Felix
  • Date: 2018
  • Subjects: Phosphogypsum , Leaching , Kinetics
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/286415 , uj:30991 , Citation: Mashifana, T., Ntuli, F. & Okonta, F. 2018. Leaching kinetics on the removal of phosphorus from waste phosphogypsum by application of shrinking core model. South African Journal of Chemical Engineering, 27:1-6. https://doi.org/10.1016/j.sajce.2018.11.001
  • Description: Abstract: This study investigated the removal of phosphorus from waste phosphogypsum by using citric acid as a leaching reagent, evaluated the potential environmental effect of the final product produced and provide recommenda- tions for the application of developed products. A dissolution process was applied and three variables were studies namely, concentration, stirring speed and temperature. The results showed that Phosphorus can suc- cessfully be removed from waste phosphogypsum and the optimum leaching conditions were at the con- centration of 0.5 M and temperature of 40 °C, with no effect observed on varying the stirring speed. Shrinking core model (SCM) was used to determine the best fit for the experimental data. For the pore diffusion model (KD), all correlation coefficients yielded were above 0.9, illustrating a positively linear correlation of KD and leaching behavior for phosphorus. Pore diffusion proved to be the effective rate controlling mechanism for the removal of phosphorus from phosphogypsum. The analysis of moments of particle size distribution (PSD) also showed a reduction in particle size, indicating the dissolution of the solid particles. The application of Toxic Leaching Characteristic Procedure (TLCP) showed low concentrations on the effluent, indicating that the de- veloped product will not contaminate the environment through leaching. The obtained leachate concentrations were within the South African effluent discharge standards. The results also showed that dissolution had a significant contribution on the moments of particle size distribution, in terms of the volume, surface area and particles number. In respect to unconfined compressive strength the products developed can be used for load bearing and as backfill material.
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Analysis of the biogas productivity from dry anaerobic digestion of organic fraction of municipal solid waste

- Matheri, Anthony Njuguna, Sethunya, Vuiswa Lucia, Belaid, Mohamed, Muzenda, Edison, Ntuli, Freeman

Influence of open porosity, hydration products and extent of hydration on the strength of desilicated lime fly ash composites

- Falayi, Thabo, Okonta, Felix Ndubisi, Ntuli, Freeman

  • Authors: Falayi, Thabo , Okonta, Felix Ndubisi , Ntuli, Freeman
  • Date: 2017
  • Subjects: Multivariate analysis , Hydration products , Open porosity
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/249019 , uj:25908 , Citation: Falayi, T., Okonta, F.N. & Ntuli, F. 2017. Influence of open porosity, hydration products and extent of hydration on the strength of desilicated lime fly ash composites.
  • Description: Abstract: The prediction of strength of lime ash composites is critical for quality control, material performance monitoring and material serviceability limit state. A study was conducted to investigate the influence of open porosity (an index of micro grain alignment and macro particle parking), sum of hydration products and extent of hydration of desilicated fly ash (DFA) on the unconfined compressive strength (UCS) of DFA lime composites. A comparison with as received fly ash (FA) was also done. The wet and dry cycle durability of DFA and as received FA composites was also investigated. The DFA and FA composites were found to have a UCS of 8.6 MPa and 7.9 MPa respectively. The FA composite was found to be more durable than the DFA composite as after 10 wet and dry cycles the composites had a UCS of 3.5 and 1.8 MPa respectively. Statistical correlation between UCS and open porosity, extent of FA/DFA hydration and sum of hydration products was implemented by Multivariate analysis. For both FA and DFA it was observed that the three parameters combined (open porosity, extent of FA/DFA hydration and sum of hydration products) had the greatest influence on the UCS than individually. This study shows that no single parameter on its own can adequately be used to predict UCS of FA/DFA lime composites. Correlation coefficients above 0.98 were found to describe the relationship between the three parameters and UCS for each composite. Thus could account for differences in durability or soaked strength of materials with equal initial dry strength.
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Sewage sludge charcoal production by N2-and CO2-torrefaction

- Hernández, Ana Belén, Okonta, Felix, Ntuli, Freeman

  • Authors: Hernández, Ana Belén , Okonta, Felix , Ntuli, Freeman
  • Date: 2017
  • Subjects: Waste-to-energy , Sewage sludge management , Thermal valorization
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/246156 , uj:25512 , Citation: Hernández, A.B., Okonta, F. & Ntuli, F. 2017. Sewage sludge charcoal production by N2-and CO2-torrefaction.
  • Description: Abstract: The production of sewage sludge charcoals under N2 and CO2 as torrefaction atmosphere and their subsequent combustion was compared in this work. The experiments were carried out in a Thermogravimetry-Infrared Spectrometry (TGA-FTIR) analyser and a laboratory scale furnace. High temperatures (230–480 °C) were considered in order to study the removal of N- and S-compounds, one of the main concerns for the thermal valorisation of sewage sludge. Torrefaction treatment at 330 °C under N2 produced a charcoal with a 34% reduction in weight. The release of SO2 during the combustion of this charcoal was negligible and the release of NH3 and COS was reduced by half (46% for NH3 and 5! 2.5% for COS) compared with the combustion of raw sewage sludge. The pollutant removal improved with torrefaction temperature and the charcoal produced at 480 °C released a negligible amount of NH3, COS and SO2 during combustion. The CO2 used as torrefaction atmosphere exhibited a reactive behaviour in the FTIR-TGA analyser, increasing the weight loss rate and shifting the characteristic degradation peak to a temperature around 7 °C lower. Besides, the charcoals produced under CO2 exhibited a less reactive behaviour. Overall, the results here presented prove that the CO2 influences slightly the torrefaction mechanisms and the properties of the sewage sludge charcoals produced.
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Thermal decomposition of sewage sludge under N2, Co2 and air : gas characterization and kinetic analysis

- Hernández, Ana Belén, Okonta, Felix, Ntuli, Freeman

  • Authors: Hernández, Ana Belén , Okonta, Felix , Ntuli, Freeman
  • Date: 2017
  • Subjects: Thermogravimetric analysis , Bioenergy , Waste treatment
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/246190 , uj:25515 , Citation: Hernández, A.B., Okonta, F. & Ntuli, F. 2017. Thermal decomposition of sewage sludge under N2, Co2 and air : gas characterization and kinetic analysis.
  • Description: Abstract: Thermochemical valorisation processes that allow energy to be recovered from sewage sludge, such as pyrolysis and gasification, have demonstrated great potential as convenient alternatives to conventional sewage sludge disposal technologies. Moreover, these processes may benefit from CO2 recycling. Today, the scaling up of these technologies requires an advanced knowledge of the reactivity of sewage sludge and the characteristics of the products, specific to the thermochemical process. In this study the behaviour of sewage sludge during thermochemical conversion, under different atmospheres (N2, CO2 and air), was studied, using TGA-FTIR, in order to understand the effects of different atmospheric gases on the kinetics of degradation and on the gaseous products. The different steps observed during the solid degradation were related with the production of different gaseous compounds. A higher oxidative degree of the atmosphere surrounding the sample resulted in higher reaction rates and a shift of the degradation mechanisms to lower temperatures, especially for the mechanisms taking place at temperatures above 400 C. Finally, a multiple first-order reaction model was proposed to compare the kinetic parameters obtained under different atmospheres. Overall, the highest activation energies were obtained for combustion.This work proves that CO2, an intermediate oxidative atmosphere between N2 and air, results in an intermediate behaviour (intermediate peaks in the derivative thermogravimetric curves and intermediateactivation energies) during the thermochemical decomposition of sewage sludge. Overall, it canbe concluded that the kinetics of these different processes require a different approach for their scaling up and specific consideration of their characteristic reaction temperatures and rates should be evaluated.
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Waste to energy bio-digester selection and design model for the organic fraction of municipal solid waste

- Matheri, Anthony Njuguna, Mbohwa, Charles, Ntuli, Freeman, Belaid, Mohamed, Seodigeng, Tumisang, Ngila, Jane Catherine, Njenga, Cecilia Kinuthia

Characterisation of fruits and vegetables wastes in the city of Johannesburg

- Ayeleru, Olusola Olaitan, Ntuli, Freeman, Mbohwa, Charles

  • Authors: Ayeleru, Olusola Olaitan , Ntuli, Freeman , Mbohwa, Charles
  • Date: 2016
  • Subjects: Fruits , Johannesburg market , Vegetables
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://ujcontent.uj.ac.za8080/10210/388885 , http://hdl.handle.net/10210/214113 , uj:21237 , Citation: Ayeleru, O.O., Ntuli, F & Mbohwa, C. 2016. Characterisation of fruits and vegetables wastes in the city of Johannesburg.
  • Description: Abstract: Municipal solid waste (MSW) composition study is very important as a baseline to utilizing fresh fruit and vegetables (FFVs) wastes in waste to energy (WtE) project. The aim of this paper is to determine the composition of various waste components at the Johannesburg FFVs market. The study was conducted during the summer in 2015 to evaluate the various components of fruit and vegetable wastes (FVWs) generated at the market. This was done in order to evaluate the amount of FVWs that are generated daily at the market as a starting point for waste to energy (WtE) proposition for the City of Johannesburg (CoJ). Two international standards: ASTM D5231-92 - 2008 (American Standard Test Method) and UNEP/IETC -2009 (United Nations Environment Programme/International Environmental Technology Centre) were used as yardsticks for the procedure used. Samples were classified based on their colours; green (vegetables and fruits), blue/purple (vegetables and fruits), tan/brown (vegetables and fruits), yellow/orange (vegetables and fruits), red (vegetables and fruits) and other wastes which include corrugated boxes, metals, woods, plastic crates and other composite wastes. Samples were further classified into 135 classes in which some were not available due to seasonal variation and the samples were manually sorted by hands. From the results of the analysis, fruits constituted 55%, vegetables 38%, corrugated boxes and cartons 3%, metals, plastics, woods and other wastes all constituted 1% each.
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Municipal solid waste composition determination in the city of Johannesburg

- Ayeleru, Olusola Olaitan, Ntuli, Freeman, Mbohwa, Charles

Utilization of organic fraction of municipal solid waste (OFMSW) as compost: a case study of Florida, South Africa

- Ayeleru, Olusola Olaitan, Ntuli, Freeman, Mbohwa, Charles

Characterization and pre-treatment of water from the Vaal River

- Vessal, Ali R., Ntuli, Freeman, Ngoie, Sonia K.

  • Authors: Vessal, Ali R. , Ntuli, Freeman , Ngoie, Sonia K.
  • Date: 2015-07-14
  • Subjects: Water quality , Vaal River (South Africa) , Water - Pollution - Control
  • Type: Article
  • Identifier: uj:5242 , http://hdl.handle.net/10210/14842
  • Description: Extensive urbanization, economic development, and industrialization coupled with water wastage are placing increased pressure on the quality of water from the Vaal River system. This research study was carried out to assess the water quality of the Vaal River in terms of physico-chemical parameters and heavy metals concentration. Three (3) locations were identified within the Upper Vaal Water Management Area (WMA) where water samples were collected in the months of July and September 2014. A total of eight water quality parameters namely pH, Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Total Hardness (CaCO3), Chemical Oxygen Demand (COD), Nitrate (NO3-), Phosphate (PO43-), Sulphate (SO42-) and Heavy Metals concentration were measured in the laboratory using standard analytical procedures. Values of measured parameters were then compared with the South African water quality guidelines for domestic use and aquatic ecosystems. The findings showed that all the physico-chemical parameters and heavy metals concentration measured were within the tolerable limits except nitrate which exceeded the recommended limit of 6 mg/l, with values ranging from 30-31 mg/l in July and 19-21 mg/l in September. The analytical data also indicated that after pre-treatment of the water sample by filtration and adsorption, the TSS level, TDS concentration, and nitrate content were significantly lowered. Nitrate was reduced to below the acceptable limit after treatment. It was therefore concluded that the river water in the Upper Vaal Water Management Area was not suitable for domestic purposes without any form of treatment and frequent monitoring of physico-chemical parameters is imperative in order to have a full representation of the variations in the water quality.
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Adsorption, kinetic and thermodynamic study of Al, Mn and Fe adsorption with natural attapulgite

- Ntuli, Freeman, Falayi, Thabo, Mabasa, Cyril

  • Authors: Ntuli, Freeman , Falayi, Thabo , Mabasa, Cyril
  • Date: 2015
  • Subjects: Attapulgite , Aluminum , Manganese , Iron , Adsorption
  • Type: Article
  • Identifier: uj:5126 , ISBN 978-1-61804-270-5 , http://hdl.handle.net/10210/14089
  • Description: Natural attapulgite was utilized as an adsorbent for the removal of Al, Fe and Mn from a mixed metal effluent. Adsorption experiments were carried out by agitation of a fixed amount of attapulgite with a fixed volume of effluent waste stream in a thermostatic shaker for varying times. Attapulgite showed that it was capable of neutralising the acidic waste stream effluent as pH after 3 hour rose from 2 to 7.46. 4% solid loading of attapulgite could remove 85% Mn(II), 90% Al(III) and 100% Fe(III) The experimental data best fit Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and the adsorption mechanism was physisorption. The adsorption process fitted well the pseudo second order kinetics for all metal ions studied. Thermodynamic data showed that Fe(III) and Mn(II) adsorption was thermodynamically spontaneous whilst Al(III) was not thermodynamically spontaneous. The process is endothermic for all metal ions. An increase in temperature resulted in an increase in spontaneity of the adsorption process. An increase in metal concentration resulted in an increase in amount of metal ion adsorbed per unit weight of attapulgite.
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Kinetic and thermodynamic parameters of silica leaching from Camden power station fly ash

- Falayi, Thabo, Ntuli, Freeman, Okonta, Felix Ndubisi

  • Authors: Falayi, Thabo , Ntuli, Freeman , Okonta, Felix Ndubisi
  • Date: 2015
  • Subjects: Fly ash , Leaching , Potassium silicate , Silicate leaching
  • Type: Article
  • Identifier: uj:5142 , ISBN 978-1-61804-270-5 , http://hdl.handle.net/10210/14120
  • Description: Fly ash from a South African power station ash dam was used. The fly ash approximated Class F fly ash but had a loss on ignition greater than 6%. The leaching parameters investigated were leaching time, KOH concentration, agitation speed, fly ash particle size, leaching temperature and liquid solid ratio (L/S). It was found that the optimum leaching conditions were leaching time of 6 h, 3M KOH, 500 rpm agitation speed, 25 L/S ratio, leaching temperature of 100˚C. Silica leaching followed a modified Jander equation kinetics with an N value of 1.48 and an activation energy of 5.9 kJ/mol.
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Adsorption of Cu and Ni from AMD using activated bentonite

- Ntuli, Freeman, Falayi, Thabo, Molala, Panelope

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