| dc.description.abstract | In recent years, the increase in world population and the rapid industry growth has led to an increased demand for water. Given the impact climate change has had on water resources, the ability to supply sufficient and safe water has become a challenge. This issue has been given more focus and increased research and one solution is to reuse wastewater for nutrients, enenrgy and other retrievable substances. In order to reuse the wastewater, it has to be treated to a certain level of quality. Therefore, a lot of different treatment technologies have been tested. One of these technologies is the gravity-driven membrane (GDM) filtration, as it provides ultrafiltration of the wastewater and is a low cost and maintenance technology.
In this experiment, a small scale GDM reactor (GDMR) ran for 96 days. The system had full sludge retention, which meant it had a very high sludge retention time (SRT). The main goals for the experiment was achieving stable flux by forming a biofilm (or biofouling layer) on the membrane and efficient nutrient removal. The wastewater used in the system was synthetic and had been pre-treated by an upflow anaerobic sludge blanket (UASB) reactor.
The reactor ran smoothly during the duration of the experiment and achieved both stable flux and permeability, despite the varying water column. The stabilized flux was achieved at day 29 in a range of 0.69 to 0.74 L/h*m2. Near the end of the experiment the flux and permeability increased to 1.03 L/h*m2 and 0.38 L/h*m2*kPa, which was due to some sloughing of the biofilm. The flux never decreased to 0 L/h*m2, so fouling never occurred during the experiment.
Concentrations for total chemical oxygen demand (tCOD) and soluble chemical oxygen demand (sCOD) were 226 ± 12 mg/L, with a percentage removal of 16% and 1% respectively. The concentrations of nitrite nitrogen (NO2-N) and nitrate nitrogen (NO3-N) increased and overall they were 6.9 ± 1.1 mg/L and 2.4 ± 0.4 mg/L. The concentration of total nitrogen (TN) and ammonium nitrogen (NH4-N) decreased a bit and overall ended up on 42.3 ± 3.9 mg/L and 31.6 ± 4.0 mg/L. For total phosphorus (TP) and orthophosphatePO4-P, the concentrations were 19 ± 0.5 mg/L and 18 ± 0.5 mg/L. Overall, the nutrient removal was poor as most of the concentrations increased or there were very little removal. The biggest reason for this is the nitrification that occurred in the reactor.
The GDMR required no maintenance during the experiment and could have ran for much longer than the 96 days. This makes it suitable to use in places where there are limited personnel to maintain and control the system. However, there should be some further testing of the system with some minor adjustments made to ensure there is passive aeration. Making sure there will not be constant overflow is also a priority, as that happened during the experiment and the inlet tank became a second bioreactor due to biomass and microorganisms growing in the tank. | |