Vahelduvaeratsiooni mõju uurimine bioloogilisele reoveepuhastusele

Käesoleva töö raames uuriti vahelduvaeratsiooni mõju bioloogilisele reoveepuhastusele. Töös anti ülevaade olulistest reovee omadustest ning puhastusprotsessidest keskendudes detailsemalt lämmastikuärastusele. Vahelduvaeratsiooni mõju uurimiseks teostati kolm laboratoorset katseseeriat kolme paralleelkatsega. Testitud aeratsiooni ajad valiti järgmised: 15 minutit, 30 minutit ja 60 minutit. Katsete efektiivsuse hindamiseks määrati proovide sisendist ja väljundist reovett iseloomustavad standard parameetrid: KHT, Nüld, NH4-N, NO2-N, NO3-N, Püld, PO4-P. Katsed teostati Tallinna Tehnikakõrgkooli laboris. Teostatud protsessid modelleeriti matemaatiliste mudelite abil tarkvaras Dynamita SUMO. Katsete analüüsi käigus tehti kindlaks erinevate aeratsiooni aegade positiivne ja negatiivne mõju lämmastikuärastusele ning õhukulule. Õhukulu on otseseks indikaatoriks protsessi energiaefektiivsusele. Uuringute tulemustes selgus, et vahelduvaeratsioon mõjub sõltuvalt puhastustsükli ajast lämmastikuärastusele erinevalt. Üldlämmasiku eemaldusele mõjus paremini 15- ja 30-minutilised aeratsiooni ajad. Matemaatilise mudeli andmeil 30-minutiline aeratsiooni aeg. Ammooniumi eemaldus oli efektiivne kõigil juhtudel, kuid nitriti oksüdeerimine ning nitraadi redutseerimine oli pärsitud. Esines asjaolu, et lühemaajalised aeratsiooni perioodid pole piisavad, et tagada efektiivne nitrifikatsiooni teise etapi lõpuni kulgemine. Sellegi poolest andis 30-minutiline puhastustsükkel märgatavalt paremaid tulemusi. Denitrifikatsiooni toimimine oli mõjutatud madalast orgaanika sisaldusest uuritava reovee koostises Vahelduvaeratsiooni mõju õhukulule oli hinnatav ainult koostatud mudeli põhjal. Summaarne aeroobne aeg protsessis oli kõigis katsetes sama, kuid õhukulu suurenes siiski aeratsiooni ajahetke pikenedes ehk suurim õhukulu esines 60-minutilise aeratsiooni tsükli katsetamisel. Antud uuring esitleb vahelduvaeratsiooni võimalikku potentsiaali reoveepuhastuse efektiivsuse tõstmisel. Uuringu käigus saadud tulemused võimaldavad reoveepuhasti optimeerimisel teha parendusi, mis võivad soodustada saasteainete eemaldamist tehes seda samal ajal ka energiatõhusamalt.

The biological removal of nitrogen in wastewater treatment plants requires the plant to ensure that necessary prerequisites for effective nitrification are obtained. This calls for continuously keeping a dissolved oxygen concentration of 1,5-2 mg/l in biological treatment. Process aeration accounts for more than 50% of the total energy consumption of the wastewater treatment plant and the latter depends mainly on the applied ventilation system. However, in the case of denitrification, it is assumed that nitrate is not removed if the wastewater contains dissolved oxygen. In order to increase energy efficiency, a more flexible treatment is needed. Earlier studies have shown that intermittent aeration is often more efficient on the removal of total nitrogen than traditional systems. The purpose of this thesis „Impact of intermittent aeration on biological wastewater treatment“, is to study the impact that short intermittent aeration cycles have on the biological wastewater treatment, in particular the removal of nitrogen and therefor how different cycles affect oxygen consumption. In order to solve the corresponding objective, a set of laboratory tests were conducted testing 15-, 30- and 60-minute aeration cycles over 4h. The parameters determined in the process were COD, TN, NH4-N, NO2-N, NO3-N, TP, PO4-P. To assess the impact of selected treatment modes in a full-scale wastewater treatment plant, mathematical models were created with modelling software Dynamita SUMO. Several important wastewater topics were described such as the properties and composition of wastewater, their importance and impact on treatment processes and an overview of wastewater treatment technologies was given. In the analysis part, positive and negative effects of various aeration cycle times on nitrogen removal and air consumption were identified. Air consumption is a direct indicator of the energy efficiency of the process. The results showed that 15- and 30-minute aeration cycle worked better for the removal of total nitrogen, removing respectively 10,7 and 10,1 mg of nitrogen. Mathematical model indicated that 30 minutes of aeration time was the most effective. On average a 92,2% decrease was seen on ammonium removal, but nitrite oxidation and nitrate reduction were inhibited. This indicates that short-term aeration periods are not sufficient enough to ensure effective second step of the nitrification carried out by Nitrobacter. SUMMARY 28 The analysis of air consumption was possible only on the basis of the mathematical model. The total aerobic time in the process was the same in all experiments, but air consumption increased in correlation with aeration cycle time, i.e. the greatest air consumption occurred during a 60-minute aeration cycle. The results obtained during this study allow improvements to be made when optimizing the wastewater treatment plant, which can contribute to the removal of pollutants while doing so more energy-efficiently.