• Drying does not affect the nutrient content and calorific value of faecal sludge. • Drying leads to a modification of the chemical form of nitrogen in faecal sludge. • Moisture removal during drying decreases the thermal conductivity and heat capacity. • Dried sludge is heated at a faster rate compared to when it is wet. • Dried faecal sludge has the potential to be reused as organic fertilizer or biofuel.

Shear rheological properties of fresh human faeces with different moisture content

This paper describes a case study undertaken at the Faculty of Engineering of the University of KwaZulu-Natal to determine the leaving rates from the faculty both by a cohort analysis (over the existence of the university from 2005 to 2010) and by a 1-year population balance over the whole faculty in 2009. Students who had left the faculty who could have continued were identified from the population balance and interviewed to determine the common reasons for leaving. The cohort analysis showed that from 2005 through to 2008, the leaving rate from first-year cohorts was reduced year on year (from over 22% to below 14%). This reduction coincided with stabilisation of the faculty after a merger process and increased academic support. In 2009, however, an increase in the proportion of first-year students who left (to over 17%) was identified, which may be linked to the entry of students who had taken the new National Senior Certificate in South African high schools. The population balance over the year 2009 showed an academic exclusion rate of approximately 6% of the total undergraduate student body, and, more significantly, an academic leaving rate of about 14% of the total student body. The exclusion rate remained fairly static across three semesters whilst voluntary leavers increased over the same period. An analysis and interviews with a sample of the students who left showed that financial reasons played a significant role in these rates, with 49% of non-academically excluded students having financial difficulties, and that a significant proportion of students continue their studies at universities of technology. Although this is a case study within one institution, it is hoped that the findings can inform the current debate surrounding increasing throughput in Science and Engineering within the country.

A thermo-chemical treatment method was used to produce biogenic amorphous silica from South African sugarcane and maize residues. Different fractions of South African sugarcane (leaves, pith, and fiber) were processed for silica production. The biomass samples were leached with either 7 wt% citric acid or 7 wt% sulfuric acid at 353 K for 2 h prior to being rinsed, dried and combusted using a four-step program ranging from room temperature to 873 K in a furnace. The characterization of the pre-treated biomass samples was conducted using thermogravimetric analysis (TG/DTA), X-ray fluorescence analysis (XRF) and elemental analysis (CHN), while the final products were characterized by XRF, X-ray diffraction (XRD), elemental analysis, nitrogen physisorption and scanning electron microscopy (SEM). Citric acid pre-treatment proved to be an attractive alternative to mineral acids. Amorphous biogenic silica was produced from sugarcane leaves in good quality (0.1 wt% residual carbon and up to 99.3 wt% silica content). The produced biogenic silica also had great textural properties such as a surface area of up to 323 m² g⁻¹, average pore diameter of 5.0 nm, and a pore volume of 0.41 cm³ g⁻¹.

This work aims at characterizing the rheological properties of faecal sludge from Ventilated Improved Pit (VIP) latrines and their implication on pit emptying. Faecal sludge was sampled from 3 pit latrines located in the eThekwini Municipality (Durban, South Africa). Samples were taken at different positions within the pit. For each of the samples, measurements in the rheometer in triplicates were performed in order to determine their rheological properties, and their moisture and ash content were measured also in triplicates. Experiments in the rheometer were performed for samples for which its moisture content was modified. In order to better understand the influence of water addition into the pit. During pit emptying, calculations were carried out from the experimental data, based in the criteria set in the Omni-Ingestor initiative, carried out by the Bill & Melinda Gates Foundation. Faecal sludge exhibited a shear thinning behaviour, i.e. a decrease in viscosity with increasing shear rate, and presented a yield stress comprised between 500 to 1000 Pa. This needs to be surpassed in order to overcome the elastic resistance of the sludge to flow. Similar viscosities were found for the samples from the different pits, irrespective of the position within the pit, except for the sample from the bottom of one of the pits for which it was not possible to induce a flow. This sample had a considerably lower moisture content (67% wet basis) compared to the other samples (around 80% wet basis), probably due to a higher biodegradation as it was the most aged sludge in the pit. According to the experimental results and calculations, the pumping requirements during pit emptying will decrease drastically by increasing the moisture content of the sludge. The addition of water into the pit would then facilitate the pit emptying operation by reducing the head and power required for pumping. However, this practice would require employing considerable amounts of water and handling higher volumes of sludge, which would lead to longer pit emptying times and increase the difficulty of the operation. For example, increasing the moisture content of the sludge from 75 to 90% will reduce the head and power of the pump by a factor 100, but will triplicate the amount of water in the sludge and, consequently, the time for pit emptying. Therefore, a compromise has to be made between increasing the pumping feasibility and adding water to the pit.

Sugarcane leaves were used to produce high-purity and low-density silica xerogels through a sol–gel method. The biogenic silica produced through a thermochemical method was reacted with sodium hydroxide (NaOH) to form sodium silicate and the produced sodium silicate was titrated with 1 M citric acid to form silica gel. The formed silica gel was washed, subjected to a solvent exchange process and later dried at 80 °C to produce low-density and high-purity silica xerogels. The produced xerogels were characterized with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), nitrogen physisorption, elemental analysis (CHNS), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The produced silica xerogels had an amorphous structure and purity of 99.9 wt%. In addition, the textural properties analysis showed that the xerogel has a BET surface area of 668 m²·g⁻¹, an average pore diameter of 7.5 nm, a pore volume of 1.26 cm³·g⁻¹ and a density of 0.23 g·cm⁻³.