Λειτουργία πιλοτικού συστήματος βιοαντιδραστήρα υπερδιηθήσεως στην επεξεργασία αστικών λυμάτων

Abstract

A pilot scale hollow-fiber ultrafiltration unit (ZW-10) was initially installed in the wastewater treatment plant of Rethymno and then transferred in the wastewater treatment plant of Chania, Crete, Greece. The system was initially fed with treated unchlorinated effluent. While the system was in Rethymno three sets of experiments were conducted. At first, the UF pilot unit was operated as a direct filtration unit. During the second phase, ultrafiltration was combined with the addition of a coagulant (Alum). The last phase of this set of the experiments involved the addition of activated carbon (either powdered or granular) into the system. During direct filtration, the average COD removal was 19%, while the average DOC was removed to a similar extent (25%). Effluent turbidity was practically independent of theinfluent turbidity values with an overall average removal of 90%. Faecal and Total coliforms were also removed efficiently reaching average removals of 99.94% and 99.96%, respectively. Removal of heavy metals in particulate form also took place. When ultrafiltration was combined with in-line coagulation, the results were very similar to those exhibited without coagulation. Combining ultrafiltration with powdered activated carbon resulted in DOC removal as high as 60%. However, after the addition of the PAC, the trans-membrane pressure increased rapidly due to the formation of PAC cake on the membrane surface. Application of granular activated carbon resulted in 36% reduction of DOC without causing an increase to the transmembrane pressure. Heavy metals present in the secondary effluent were also removed very efficiently by the GAC in the UF tank.The system was then transformed into a Membrane Bio Reactor (MBR). The treatment took place with biomass concentration (MLSS) 5 mg/L provided a high level of treatment for primary municipal wastewater. The removal of SS reached 99.99% resulting in a MBR effluent with SS levels below 1 mg/L. This demonstrated excellent solids separation achieved by the UF membrane. Similar removal levels were achieved for turbidity (99.72 %). The average COD removal was 97.3% resulting in an effluent with COD ranging between 8-32 mg/L. However, relatively low Total Nitrogen removal (TN) was achieved with most likely mechanism fornitrogen removal nitrogen assimilation in the biomass. Heavy metal removals were very high: Pb and Ni were removed completely indicating that these two metals were in particulate form, while Cr and Cu were removed by 89% and 49%, respectively. Combination of MBR and Reverse Osmosis (RO) was then conducted. The combination provided a superb quality effluent devoid of heavy metals and with very low organic matter concentration (DOC level below 4 mg/L). Yet, Total Nitrogen removal was not complete resulting in a TN concentration around or less than 20 mg/L. The next part of the research was focused on the treatment of the concentrate produced from the lab scale RO system treating the pilots scale MBR effluent.Chemical processes such as coagulation with Alum and FeCl3 and adsorption into granular activated carbon were tested. Advanced Oxidation Processes (AOPs) such as electrolysis, photocatalysis and sonolysis were also applied. DOC was measured for every sample. Satisfactory results were obtained from the AOPs but higher removals of DOC were achieved via chemical processes.In the last part of the experiments, ultrafiltration membrane is tested for the removal capability of some major endocrine disruptors. The pharmaceuticals under research were carbamazepine, chlofibric acid, triclosan, 17α-ethynil-estradiol and 17β-estradiol. Mass balances were carried out in order to calculate the amounts of the substances that were biodegradated or adsorbed in the biomass. The results showed very high adsorption of the substances in the biosolids and limited biodegradation.