Design and Optimization of Sedimentation Tank Coupled with Inclined Plate Settlers as a Pre-Treatment for Ultra-Filtration

Access to clean and safe drinking water is difficult in most rural areas of Sub-Saharan Africa. In most places, the water is generally available during the rainy season, but it is muddy and full of sediments. But in Karatu, regardless of the season, the water is always highly turbid with suspended particles. High turbidity water is a great challenge to water treatment works as it can be hard to remove and also harbors pathogens. Because of a lack of cost-effective purifying agents, communities suffer from water scarcity or indeed drink water that is no doubt contaminated by sediment and livestock/human feces. Unsafe drinking water is a major cause of water-related diseases that predominantly affect people living in developing countries. Today there are many technologies available to treat unsafe water. However, most of such technologies are suited for use with low turbidity source water. Ultra- Filtration (UF) is one technology which is limited to treating high turbidity water. The pre-treatment of high turbidity water (>1000 NTU) is a challenge that was investigated in this research. This paper describes a laboratory scale sedimentation tank coupled with Inclined Plate Settlers (IPS) tested and optimized at Nelson Mandela African Institution of Science and Technology (NM-AIST), to see if, given the local particle sizes and distribution in the earthen dam water of Karatu, IPS can pre-treat the raw water to remove enough turbidity to make UF a feasible option. The results of this work show that IPS is not only a feasible option in pre-treating highly turbid water for the UF (˂ 50 NTU) but also a viable technology in treating water with very high turbidities to within the Tanzania drinking water standards (< 25 NTU). Keywords: High turbidity water; Sedimentation tank; Inclined Plate Settler; Ultra-Filtration; Water suppl

Optimization of Sedimentation Tank Coupled with Inclined Plate Settlers as a Pre-treatment for High Turbidity Water

Access to clean and safe drinking water is a challenge in most rural areas of Tanzania. Unsafe drinking water is a major cause of water-related diseases that predominantly affect people living in developing countries. In most places, water is readily available during the rainy season, but it is muddy and full of sediments. But in Karatu, regardless of the season, water is always highly turbid with suspended particles. High turbidity water is a great challenge to water treatment works as it can be hard to remove and also harbors pathogens. Because of a lack of cost-effective purifying agents, communities suffer from water scarcity and use water that is no doubt contaminated by sediment and livestock/human feces. Today there are many technologies available to treat unsafe water. However, most of such technologies are suited for use with low or no turbidity source water. Ultra- Filtration (UF) is very effective in making unsafe water safe through removal of chemical species and pathogens. UF, however, like many other treatment techniques, is limited to treating water with high turbidity. Pre-treatment is needed. The pre-treatment of high turbidity water (>1000 NTU) is a challenge that was investigated in this research. This paper describes a laboratory scale sedimentation tank coupled with Inclined Plate Settlers (IPS) tested and optimized at NM-AIST, to see if IPS can pre-treat the raw water to remove enough turbidity to make UF a feasible option. The results of this work show that IPS is not only a feasible option in pre-treating highly turbid water for the UF (˂ 50 NTU) but also a viable technology in treating water with very high turbidities to within the Tanzania drinking water standards (< 25 NTU). The design is ready for pilot testing in field environment. Keywords: High turbidity water, Sedimentation tank, Inclined Plate Settler, Ultra-Filtration

Approaches to the mitigation of ammonia inhibition during anaerobic digestion – a review

This research article published by IWA Publishing, 2020The digestion process of organic waste rich in high ammonia content has always been a gridlock during methanogenesis process. The free ammonia may increase inhibition/toxicity, which in turn affects the microbial community in the digester and eventually leading to process failures. Substantial methods have been proposed and assessed for curtailing ammonia emissions in anaerobic digesters to attain a safe and steady process so that along with high methane production, high quality of effluents can also be recovered. There are several means for lowering the erratic ammonia in organic wastes which has been in use currently such as the decrease of pH, which favour the formation of ammonium over ammonia in the equilibrium. For example, the use of chemical additives that attach ammonium-N. Ammonia can also be removed from nitrogen-rich substrates during anaerobic digestion through other methods such as struvite precipitation, membrane distillation, air stripping, ion exchange, and adsorption. A thoroughly survey from different articles has shown that ion exchange, adsorption and changing of the C/N ratio through co-digestion technique, are the most commonly studied methods for mitigating ammonia inhibition in wastewater during anaerobic digestion. A detailed review of these methods in the context of nitrogen-rich substrates will be discussed in this paper

Modification of municipal wastewater for improved biogas recovery

This research article published by IWA Publishing, 2020The energy demand which is expected to increase more worldwide has sparked the interest of researchers to find sustainable and inexpensive sources of energy. This study aims to integrate energy recovering step into municipal wastewater treatment plants (MWWTPS) through anaerobic digestion. The anaerobic digestion of municipal wastewater (MWW) and then co-digestion with sugar cane molasses (SCM) to improve its organic content was conducted at 25 °C and 37 °C. The results showed substrate mixture containing 6% of SCM and total solids (TS) of 7.52% yielded higher amount of biogas (9.73 L/L of modified substrate). However, chemical oxygen demand (COD) of the resulting digestate was high (10.1 g/L) and pH was not stable hence needed careful adjustment using 2 M of NaOH solution. This study recommends substrate mixture containing SCM (2%) and TS (4.34%) having biogas production (4.97 L/L of modified substrate) for energy recovering from MWWTPS, since is found to have more stable pH and low COD residue (1.8 g/L) which will not hold back the MWW treatment process. The annual generation of modified substrate (662,973 m3) is anticipated to generate about 16,241 m3 of methane which produce up to 1.8 GWh and 8,193 GJ per annum

Integrated constructed wetlands treating industrial wastewater from seed production

This research article published by IWA Publishing, 2021The performance of an integrated wastewater treatment system composed of horizontal subsurface flow constructed wetland (HSSFCW), floating constructed wetland (FCW), and anaerobic baffled reactor (ABR) was studied for pollutant removal from seed production wastewater. Cyperus alternifolius (Umbrella Papyrus) plants were used in the HSSFCW, and Vetiveria zizanioides (Vetiver grass) in the FCW. The ABR was fed with 25 m3/d wastewater from its equalization tank. The average raw wastewater organic loading rate was 0.208 kg-COD/d. Grab wastewater samples were collected twice weekly for three months from each unit's inlet and outlet. The system's performance in removing biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), turbidity, nitrate, phosphate, and ammonium was studied. The average removal efficiencies obtained were 95.5% BOD5, 94.6% COD, 86.2% TSS, 76.6% turbidity, 82.4% nitrate, 76% phosphate, and 32.9% ammonium. The results show that integrating ABR, HSSFCW, and FCW improves pollutant removal from seed production wastewater, and the treated water can be used for agricultural purposes

Tracking Materials with Low Phosphorus Adsorption for Use in Constructed Wetland Aiming at Wastewater Treatment for Irrigation Purposes

Wastewater is well known to contain significant amounts of essential crop nutrients including Phosphorus (P). Therefore, in the light of water reuse, nutrients available in wastewater need to be retained to serve as alternative source of plant nutrients for the crops to be irrigated by the effluent. P-adsorption experiments of four selected locally available substrate materials (dolomite marble, andesite, basalt and scoria) were conducted in laboratory. The aim of the study was to characterize the material and determine their P-Adsorption capacity, deduce their suitability for use as substrate material for constructed wetland aiming to treat wastewater for reuse in irrigation. It also aimed at establishing the baseline information for the available materials in Arusha. The chemical composition of each of the materials was determined using the XRF analysis method, and the P-adsorption capacity of each material was determined by studying the removal rates at different known P-concentrations (5, 10, 20 and 50). Highest P-adsorption capacity was observed in dolomite marble (99-100%) and lowest in andesite (40-46%). It is therefore concluded that with the aim of retaining phosphorus in the final effluent andesite, should be selected as a suitable substrate material for constructed wetland systems

Performance of inclined plates settler integrated with constructed wetland for high turbidity water treatment

This research article published by IWA Publishing, 2021The purpose of this study was to investigate and demonstrate cost-effective treatment technologies for high turbid waters, used for domestic purposes in rural areas of Tanzania where conventional community water treatment techniques are not available. Pilot scale inclined plates setter integrated with constructed wetland (IPS-CW) system was investigated on earth dam water with turbidities ranging from 186 to 4,011 NTU. The IPS was used as a physical pretreatment system preceding the CW, meant for the removal of organic matter, nutrients, and pathogens. Major focus of the IPS-CW system was on turbidity and faecal coliform (FC) removal and at 5 L/min flow rate mean maximum removal efficiency of 95.9% and 94.3% were achieved, respectively. Total suspended solids, nitrate (NO3 ), ammonium, biological oxygen demand (BOD5) and phosphate removal were studied and removal efficiencies of 97.4%, 91.7%, 71.3%, 91.7% and 49.8% were obtained at 5 L/min flow rate, respectively. Although the use of these combinations of technologies in improving drinking water quality is uncommon, results demonstrated that NO3 and BOD5 met WHO and TBS drinking water standards of 50 mg/l and 6 mg/L respectively. Due to low production cost and simplicity in operation the system is relevant for application in rural communities

Effect of mixing ratios of natural inorganic additives in removing ammonia and sulfide in the liquid phase during anaerobic digestion of slaughterhouse waste

This research article was published in Materials Today Chemistry, Volume 20, 2021.In this study, the efficacy of inorganic additives in the removal of total ammonia nitrogen (TAN) and sulfide in the aqueous phase of slaughterhouse waste undergoing anaerobic digestion in the batch reactor was investigated. A mixture of natural inorganic additives processed from the anthill and red rock soil samples collected from Arusha, Tanzania were used as adsorbents in different ratios. These materials were chosen in regard to their abundance in the local environment, surface properties, and elemental composition. Before analysis, the materials were pulverized and calcined at 700 and 900 °C for 2 h in a furnace and then sieved to 250 μm fine particle size. XRD analysis revealed that the anthill soil sample is endowed with major mineral phases of quartz and hematite while red rock soil contains albite, pyroxene, and quartz as predominant phases. The anthill and red rock soil samples calcined at 900 °C displayed higher BET surface areas of 815.35 and 852.35 m2/g, respectively. The mixture of anthill soil and red rock soil in a ratio of 3:1 had a higher TAN removal efficiency of 92% at a contact time of 30 min compared to other ratios. On the other hand, a ratio of 1:2 showed a higher sulfide removal efficiency of 79% at a contact time of 60 min. Adsorption isotherm studies revealed that the Jovanovich model fitted better to the experimental data than the Langmuir and Freundlich models. The results demonstrated further that inorganic additives have a synergistic effect on stimulating methanogenesis as well as eliminating ammonia and sulfide during anaerobic digestion of slaughterhouse waste. Our findings demonstrate that anthill and red rock soils can be exploited as affordable, ecofriendly, and efficient adsorbents for mitigation of TAN and sulfide from the liquid phase and sustenance of methanogenesis

Evaluating the level of ammonia and sulfide in the liquid phase during anaerobic digestion of slaughterhouse waste operating at mesophilic scale digester—the impact of inhibition and process performance

This research article published by AIMS Press, 2020The performance of experimental batch-reactor loaded with slaughterhouse waste at mesophilic temperature was investigated as well as the inhibition of both ammonia and sulfide concentration in the aqueous phase. The digester was operated for 68 days by evaluating the process stability basing on controlling parameters such as pH, volatile fatty acids and alkalinity in relation to the methane produced. The maximum CH4 content of 69.6% was achieved at 0.37 VFA/Alkalinity ratio and pH of 7.51 during day 37 of anaerobic digestion. However, a sudden increase of ammonia nitrogen in the digester from day 44 to day 68 decreased the methane content about 62.15% from 65% to 24.6%. Similarly, as the amount of sulfide content decreased in the liquid phase, gaseous H2S was elevated up to 132 ppm in the 68th day. During this time, it was observed that the ratio of VFA/Alkalinity decreased to 0.16, with a very low concentration of VFA, which was 150.92 mg/L. This phenomenon indicated that all the acids produced were consumed by methanogens and ammonia inhibition was at the highest rate due to the increase of ammonia nitrogen concentration in the last days of digestion. Furthermore, among of peculiar characteristic shown by slaughterhouse waste is the ability to maintain the pH above 7 without the addition of any buffering agent throughout the AD process. Meanwhile, the evaluation of the level of both ammonia and sulfide in the aqueous phase revealed that the inhibitory effect of ammonia concentration was higher than sulfide concentration

Life cycle analysis of potential municipal solid wastes management scenarios in Tanzania: the case of Arusha City

This research article published by Springer Nature, 2021The municipal solid wastes (MSW) management technologies in most cities of developing countries pose a continuous risk of contaminating the environment and affecting human health adversely; often because MSW technologies are not comprehensively analyzed before their implementation. For this purpose, the life cycle assessment methodology was applied to access the different MSW management scenarios in Arusha City, Tanzania. Three different scenarios of recycling and sanitary landfilling (RSL) were developed as the business as usual scenario (RSL) (SN-1), RSL combined with composting (SN-2), and RSL combined with anaerobic digestion (SN-3). Results obtained showed that no scenario performed better in all impact categories, however with the current focus on climate change and limited funds in developing countries, the best option would be SN-2. The SN-2 which is the combination of recycling, composting and the landfill had the least economic cost and environmental burdens in most categories when compared to the other scenarios. The sensitivity analysis results indicated that improving diesel consumptions, reducing methane emissions to air and increasing the recycling rate of papers and plastics would reduce the total environmental impacts on all scenarios