Aktiivmuda pundumise põhjuste analüüs ning vastumeetmete välja töötamine Kehra reoveepuhasti näitel

Aktiivmuda pundumine toob puhastile mitmeid probleeme. Nendeks on vahutamine aerotankis, aktiivmuda settimisomaduse halvenemine, kõrgemad opereerimiskulud ning hõljuvainete väljakandumist ja nii piirmäära ületamisi. Probleemide põhjuseks on filamentide koloonia tõus aktiivmudas. Antud töös keskenduti filamentide vohamise põhjuste uurimisele Kehra reoveepuhastis, saadud tulemuste analüüsimisele ning ettepanekute tegemisele. Saadud uuringu tulemustest selgus, et Kehra reoveepuhasti filamendi indeks on 5 ehk filamentide arvukus aktiivmudas on väga kõrge. Põhjused, mis võimendavad filamentide kasvu Kehra reoveepuhastis, on järgmised: reovesi viibib liiga kaua aerotankis, vähe toitu ja palju mikroorganisme ning madal lahustunud hapniku sisaldus. Märkimist vajab toitainete vähesuse probleem. Selline olukord puhastis annab kasvueelise filamentidele, sest flokimoodustajad bakterid on aeglasema kasvuga kui filamendid. Nii tarbivad filamendid kogu toidu ja flokimoodustajad ei suuda toitainete defitsiidis piisaval määral paljuneda. Filamentide vohamise probleemi on palju varasemalt uuritud. On leitud, et probleemi võib aidata lahendada aerotanki ette paigaldatav õhutusreaktor ehk selektor. Selektori eesmärk on tõsta orgaanilise aine kontsentratsiooni ja seeläbi stimuleerida flokimoodustajate kasvu. Tööpõhimõte seisneb selles, et tagastusmuda viiakse kokku sissevooluga, mille tulemusel tõuseb orgaanilise aine kontsentratsioon. Antud uurimuses leiti, et Kehra reoveepuhasti filamendi vohamisprobleemi võib leevendada õige selektori paigaldamine aerotanki ette. Selleks dimensioneeriti Kehra reoveepuhasti andmetel standardi ATV-DVWK-A 131E järgi sobiv selektor, mille ruumala on 17 m3 ja selles vajalik hapniku kogus on 68 kg O2/m3.

The title of following graduation thesis is Analysis of Activated Sludge Bulking Problems and Development of Countermeasures on the Example of the Kehra Wastewater Treatment Plant. Activated sludge process is the most common biological treatment technology for domestic and industrial wastewater treatment. The activated sludge process is based on microorganisms that are able to remove contaminants from wastewater under suitable conditions. Thus, any change in the process can have a number of negative consequences, including bulking of activated sludge. Bulking of the activated sludge begins with an increase in the colony of filaments in the activated sludge. This phenomenon causes certain problems for the treatment plant, such as: foaming in the aeration tank, deterioration of the sedimentation properties of activated sludge, higher operating costs and removal of suspended solids and thus, exceeding the limit value. The graduation thesis gives an overview of wastewater parameters, treatment technologies and the problem of activated sludge bulking on the example of the Kehra Wastewater Treatment Plant. Kehra Wastewater Treatment Plant is located in Kehra, Anija municipality, Harju County. The treatment plant have been designed to treat 4500 population equivalent. The probleem investigated in this work was foaming in the aeration tank of the Kehra wastewater treatment plant, which causes certain problems for the treatment plant. Foaming is caused by bulking of activated sludge. Thus, the aim of this graduation thesis was to study this problem in the Kehra wastewater treatment plant, to perform a thorough analysis and, consequently, to propose possible solutions. The results of the study showed that the filament index of Kehra wastewater treatment plant is 5, it means that the number of filaments in activated sludge is very high. The reasons that increase the growth of filaments in the Kehra wastewater treatment plant are the following: the hydraulic retention time in the aeration tank is too long, there is nutrient deficiency and the low dissolved oxygen content. The problem of nutrient deficiencies needs to be mentioned. This situation in the purifier gives a growth advantage to the filaments because the flocculating bacteria are slower to grow than the filaments. As a result, filaments consume whole food and flocculants are unable to reproduce sufficiently in nutrient deficiencies. In this study, it was found that the problem of proliferation of the filament in the Kehra wastewater treatment plant can be alleviated by installing the correct selector in front of the aeration tank. The purpose of the selector is to increase the concentration of organic matter and thereby stimulate the growth of flocculants. For this purpose, a suitable selector with a volume of 17 m3 and a required amount of oxygen of 68 kg O2 / m3 was dimensioned with standard ATV-DVWK-A 131E according to the data of Kehra wastewater treatment plant.