M.Sc. (Botany) / A comparison was made between the effectiveness of the biological filtering and activated sludge processes at the Johannesburg North Sewerage Works by making use of, inter alia, the physical-chemical and biological research methods. In addition to the standard physical and chemical analytical techniques, the biological growth potential technique, the lC method of determining primary productivity and biomass determination by way of the chlorophyll a method, were also used. The most important findings were: 1. that the activated sludge process purifies the water more effectively than the biological filtering process; 2. that no seasonal fluctuations affecting the effectiveness of the purifying systems were found, and 3. that the biological growth potential of the effluent in the Jukskei River was such that it could still cause algal growth. The primary recommendation is that tertiary purifying techniques will have to be employed in order to reduce The high phosphorous levels still prevailing in the effluent to comply with the requirements of the Water Act of 1984.

M.S.

Experiments were performed on samples of alum, anaerobically digested, and aerobically digested sludges to determine optimum polymer dosages for various mixing intensities produced during conditioning by a high-stress mixing unit. Mean velocity gradient (G) values were established for each of the mixing speeds used ranging from 250 sec-1 to 4,000 sec-1. Using the optimum conditioning dosages determined each mixing speed, batches of optimally, conditioned sludge were introduced into a pilot scale plate and frame filter press. Filtrate volume per unit time and final cake solids were used to characterize the press performance. Results indicated that filter press, performance can be optimized by selecting mixing. speeds during conditioning that simulate the shear conditions produced in the filter press during operation. It was shown that press performance was substantially reduced using sludge conditioned at a mixing speed of 200 rpm, corresponding to a Gt equal to 17,000. Tests using mixing speeds of 400 rpm and 1800 rpm corresponding to Gt values of 32,000 and 230,000, respectively indicated better performance and, thus, the filter press is thought to generate Gt values within this range. A substantial increase in polymer requirements is shown for sludge conditioned at a mixing speed of 1800 rpm, and therefore, it was concluded that sludge conditioned at mixing speed of 400 rpm best characterized the filter press producing optimum operational conditions. It was also postulated that the filter press may not be characterized by a single Gt value, but, by a range of values dependent on press run time. / Master of Science

The sludge blinding coefficient, β, was evaluated in this experimental study, to determine if β could be used as a useful characterization parameter for sludge filterability. Fresh activated sludge, activated sludge aged at room temperature, primary sludge, alum sludge, and a calcium carbonate slurry were filtered using a Buchner funnel apparatus and varying size filter media at various pressure differentials. Particle size measurements were also performed on the above mentioned sludges using an automated particle size analyzer to examine the impact of particle size and size distribution on β. Effects of conditioning, elutriation, supernatant removal, and replacement on β were also studied. In general, β correlated well with the average specific resistance, indicating that it could be useful in predicting a sludge filtration pattern. β was found to increase as the mean particle size of a sludge decreased, or the particle size distribution of a sludge widened. Conditioning, elutriation, supernatant removal, and replacement were found to reduce β by improving the mean particle size of a sludge and narrowing a sludge particle size distribution. In addition, β was found to increase by the applied pressure differential and filter media pore sizes for a few sludges. / Master of Science

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Submitted in complete fulfillment for the degree of Doctor of Philosophy (Biotechnology) in the Department of Biotechnology and Food Technology, Durban University of Technology, Durban, South Africa, 2016. / Many households in developing countries are still without proper sanitation systems. The problems are even more prevalent in rural communities where there are no septic systems in place for the treatment of wastewater. This has resulted in the urgent need for the development and implementation of innovative wastewater treatment systems that are inexpensive, environmental friendly and are able to reduce contaminants to levels that pose no harm to the communities. Constructed rhizofiltration systems have been explored for this purpose. They have been used for many decades in many countries with varying degrees of success at the primary, secondary and tertiary levels of wastewater treatment. Poor optimization of this technology has been due to limited information available about the roles played by the whole system as well as by each component involved in the treatment technology. The current work elucidates the role played by macrophytes and microbial biofilms in the removal of nutrients in the rhizofiltration system. Factors affecting waste removal as well as environmental friendliness of the system were also investigated. The rhizofiltration system was constructed in Durban and was divided into planted (planted with Phragmites australis and Kyllinga nemoralis) and unplanted (reference) section. Dissolved oxygen (DO), pH, water temperature, total dissolved solids (TDS), electrical conductivity (EC) and salinity were monitored. The removal efficiency of nutrients was measured using spectrophotometric methods by measuring the concentration of ammonia, nitrate, nitrite, phosphate and orthophosphate in the wastewater pre- and post-treatment. The total organic carbon, chemical oxygen demand (COD), total Kehldjahl nitrogen, biological oxygen demand (BOD), ammonia, nitrate and the flow rate of wastewater into the system from the settling tank were used for the estimation of carbon dioxide, methane and nitrous oxide emitted from the rhizofilter using the 2009 EPA formulae. Both the planted and reference sections of the system removed nutrients with varying efficiencies. The reduction of nutrients in the rhizofilter was found to be seasonal, with most nutrients removed during the warm seasons. The system also retained more nutrients when wastewater containing low levels of nutrients was used. The unpaired t-test was used to determine the differences between nutrient removals between planted and reference sections. Higher reduction efficiencies of nutrients were obtained in the planted section. Up to 65% nitrite and 99% nitrate were removed while up to 86% total phosphorus was removed in a form of orthophosphate (86%). Removal of total nitrogen was shown to increase under high temperature conditions, while the same conditions decreased the total phosphorus removal. High temperatures also increased the performance of the system. The reduction of nutrients in the system corresponded to reduction of the chemical oxygen demand which also positively correlated to the dissolved oxygen concentration. Considering the discharge limits for all nutrients, the discharges in the effluent of the planted section were within the allowable limits as per South Africa’s Department of Water affairs and Forestry in 2012 but not in 2013. The results obtained in 2013 were due to increased nutrient loading introduced into the system. Diverse microbial communities occurred in the treatment system, with more diversity in the planted section. These organisms were supported by macrophytes in the planted section, and were responsible for nitrogen and phosphorus transformation. This explains why total nitrogen and phosphorus reduction was higher in the planted compared to the reference section. Both the planted and the reference sections of the rhizofiltration system produced the greenhouse gases. When the two sections were compared, the planted section produced more gases. Gases emitted by both sections were lower when compared to emission from sludge treatment reed beds and other conventional systems of wastewater treatments. These findings indicated that constructed rhizofiltration is a cleaner form of waste treatment, producing significantly less greenhouse gases and affecting less of a climate change. Findings of this work have revealed that rhizofiltration technology can be used as a low-cost alternative technology for the treatment of wastewater, using the combination of macrophytes and microbial biofilms. Macrophytes accumulated nitrogen and phosphorus as well as supported diverse microorganisms that metabolized and reduced nutrients in the rhizofiltration unit. / D

A total of 44 intermittent sand filter-septic systems, in five counties of Western Oregon, were sampled over a three-month period during the summer of 1995. The sand filter systems varied in age from 36 months up to 167 months (3 to 13.9 years). Liquid samples were taken from the septic tank and distribution box. In addition, soil samples were taken adjacent to the disposal trench and away from the disposal field area (control). All samples were analyzed for Total Kjeldahl Nitrogen (TKN) and nitrate and nitrite. Nitrite was not detected in any of the samples. The average removal of total nitrogen (TKN + nitrate) through the filter was found to be 43%. Nitrate was determined to be the dominant form of nitrogen in the sand filter effluent making up 94% of the total nitrogen. The age of the system was found not to be a predictor of the system's performance. Once the effluent entered the disposal field, little if any transformation of nitrogen occurred at an average depth of 30 inches (76.2 cm). / Graduation date: 1996

No description available.

The object of this investigation was to determine, by the concept of specific resistance, the effect of certain variables on the filterability of calcium sulfate sludge resulting from lime neutralization of synthetic, return sludge seeded, sulfuric acid samples, The variables investigated were rate of mixing, rate of lime addition, degree of neutralization, return sludge loadings and acid concentration. Mixing rate and lime addition rate are factors effecting the characteristics and filterability of calcium sulfate sludge. Slow lime addition provided a more effective return sludge than did rapid lime addition. Slow sample mixing produced a more filterable sludge than did rapid mixing for a given lime addition rate. The degree of sample neutralization appeared to have only a minor effect on the filterability of the sludge, with the filter ability improving as the final pH of the sample decreased. The sample return sludge dosage appeared to have only a minor effect on the filterability of the resulting sludge with filterability decreasing as return sludge loadings increased. A complete evaluation of the effect of return sludge loading cannot be made, however, until these studies are expanded to include the optimum return sludge loading for the given acid-lime system. The values of specific resistance obtained were influenced by the resistance of the filter paper. For samples with similar dry solids concentration the effect is approximately the same; however, the amount of filter paper interference decrease with increased sample dry solids concentration. For varying acid concentrations there was a minor decrease in specific resistance as the acid concentration, and dry solids concentration, of the samples increased. This decrease was thought to be due to decreasing amounts of filter paper interference rather than improved sludge filterability. / Master of Science

Many soils are marginally suited for installation of on-site wastewater disposal systems. With soil limitations, additional wastewater treatment prior to soil application may allow for a reduction in soil depth. Undisturbed 20-cm-diameter soil columns (fine loamy, mixed, mesic Typic Hapludult), in a factorial arrangement between depth of soil (15, 30, and 45 cm) and type of effluent (septic tank, constructed wetlands, and recirculating sand filter), were used in this study. Effluent (670 cm³/d) was applied 6 times daily. Additional treatment of septic tank effluent by a constructed wetland and a recirculating sand filter resulted in 30 and 70% higher average soil infiltration rates, 92 and 96% reduction in fecal coliforms, 34 and 44% reduction in total nitrogen, and a 60 and 94% reduction in BOD₅, respectively. Fecal coliforms were present only in soil leachate from the 15 and 30 cm soil depths receiving septic tank effluent and the 15 cm depth that received constructed wetland effluent. Average soil leachate NO₃⁻-N concentrations were 19, 10 and 14 mg/L from soil columns receiving septic tank, constructed wetland, and recirculating sand filter effluents, respectively. Soil leachate contained <5 mg/L TKN and 1.8 mg/L NH4⁺-N. Total nitrogen losses were 55, 73, and 66 for the septic tank, constructed wetland, and recirculating sand filter treatments, respectively. BOD₅ averaged less than 4 mg/L in the soil column leachate, despite a 10 fold difference among influent types. In comparing the 1993 and 1994 growing seasons, average plant tissue dry weight, percent nitrogen, and percent phosphorus were greater during the 1994 growing season. The results from this study indicate that additional treatment of septic tank effluent can be substituted for soil depth. / Master of Science