Effect of Application of Polyaluminium Chloride on Reducing Exploitation Problems at the Wastewater Treatment Plant in Olsztyn

Abstract

WPŁYW DAWKOWANIA CHLORKU POLIGLINU NA OGRANICZENIE PROBLEMÓW EKSPLOATACYJNYCH W OCZYSZCZALNI ŚCIEKÓW W OLSZTYNIE Adam Drzewicki Katedra Ekologii Stosowanej Uniwersytet Warmińsko-Mazurski w Olsztynie Słowa kluczowe: Microthrix parvicella, puchnięcie osadu, piana pochodzenia biologicznego, organizmy nitkowate, chlorek poliglinu. Address: Adam Drzewicki, University of Warmia and Mazury, ul. Oczapowskiego 5, 10-957 Olsztyn, Poland, phone +48 (089) 524 51 07, e-mail: adam.drzewicki@uwm.edu.pl Abstrakt W pracy oceniono skuteczność stosowanych zabiegów dawkowania chlorku poliglinu (PAX-18) na poprawę właściwości sedymentacyjnych osadu czynnego w oczyszczalni ścieków w Olsztynie. Określono przyczynę puchnięcia i pienienia osadu czynnego. Przeanalizowano wpływ dozowania chlorku poliglinu na indeks objętościowy osadu czynnego (SVI) i liczebność Microthrix parvicella. Dawkowanie PAX-18 w zakresie od 0,63 do 2,13 g Al kg smod w układzie, w przedziałach czasowych od 10 do 89 dni, okazało się nieskutecznym sposobem na obniżenie SVI. Stosowane zabiegi w większości przypadków ograniczały natomiast wpienianie osadu czynnego w reaktorach wielofunkcyjnych. Introduction The technological changes broadly introduced in the 1990s to Polish wastewater treatment plants operating on activated sludge that would enable improved removal of nitrogen and phosphorus from sewage and wastewater have compounded the problem of foaming and bulking of activated sludge. This is a result of the fact that the conditions which facilitate the removal of biogens promote the development of specific forms of filamentous bacteria in activated sludge, mostly responsible for its foaming and bulking. One of the most common representative of such filamentous microorganisms is Microthrix parvicella (KALISZ et al. 2005, DRZEWICKI et. al. 2008). Excessive growth of this bacterium creates many exploitation difficulties, such as a disturbed sludge sedimentation process, difficulties in maintaining the adequate age of sludge and recirculant concentrations, impeded dewatering of sludge, inferior production of biogas, problems related to safety in closed fermentation chambers, and many other drawbacks up to inferior visual qualities of the wastewater treatment facilities. Excessive growth of Microthrix parvicella in activated sludge used for removal of biogenic substances is very difficult to halt. The bacterium proliferates well owing to the long age of sludge and associated low load. The microorganism demonstrates high affinity to oxygen (LEMMER 1992). Under both aerobic and anaerobic conditions, it is capable of binding and utilizing long-chain fatty acids, present in raw sewage, as a source of carbon atoms and energy (ANDREASEN, NIELSEN 2000, SLIIJKHUIS, DEINEMA 1988, SLIIJKHUIS et al. 1984). All these factors make it difficult to control the causes of the growth and development of Microthrix parvicella in wastewater plants using technologies for improved removal of nitrogen and phosphorus from sewage. It seems that application of polyaluminium chloride could be an effective way of controlling the bacterium. However, this is an expensive method, which also involves generation of excess sludge and can be harmful to the whole activated sludge biomass as well as to the natural environment in that that is acts selectively and creates better conditions for Effect of Application of Polyaluminium... 159 growth of subordinate filamentous organisms. Therefore, each wastewater plant needs to work out its own strategy for the frequency of application and concentration of used doses of this reagent. The purpose and scope of the study The purpose of this study has been to assess the effectiveness of adding doses of polyaluminium chloride PAX-18 in improving sedimentation properties of activated sludge in the wastewater treatment plant in Olsztyn. The study involved: – determination of the causes of foaming and bulking of activated sludge; – analysis of the effects produced by the applied doses of polyaluminium chloride on sludge volume index (SVI) and population of Microthrix parvicella. Materials and Methods The wastewater treatment plant The Łyna Wastewater Treatment Plant in Olsztyn receives from 32 to 37,000 m d of municipal sewage from the towns of Olsztyn and Barczewo as well as from four rural communes: Barczewo, Dywity, Gietrzwałd and Stawiguda. Of the total volume of received sewage and wastewater, only 0.35% is delivered in septic vehicles. Some of the characteristics of the received sewage can be found in Table 1. The plant facilities were refurbished in 2004, and now the technological line consists of two automated dense stepped screens, a horizontal grit chamber with two parallel channels, two circular Dorr type primary sedimentation tanks, a primary sludge digester, a recirculated sludge denitrification chamber, a dephosphatation chamber, five Table 1 Physicochemical characteristics of sewage according to the data supplied by the WTP laboratory Raw sewage Treated sewage 2006 2007 2008 2006 2007 2008 Parameters Units BOD5 mg O2 dm 401 583 583 5.5 7.5 4.3 CODChr mg O2 dm 664 954 973 40 50.8 58 Suspended soilds Mg dm 224 476 516 3.1 18 4.5 Nitrogen mg Nog dm-3 72 81 90 11.3 9.2 14 Phosphophrus mg Pog dm 11 17 16.8 1.5 1.3 0.9 All data are presented as means from 12 analyses performed at monthly intervals Adam Drzewicki 160 multi-functional chambers of bioreactors each equipped with four Passavant rotors, and three secondary sedimentation tanks. Sewage sludge is inactivated in two closed fermentation chambers and three open fermentation tanks to be finally dewatered on a mechanical press. The post-fermentation waters are discharged to the Łyna River. The values of pollutants in the treated wastewater are presented in Table 1. Exploitation problems The analysis of the collected information and results of own observations enable us to conclude that the exploitation problems encountered at the wastewater treatment plant in Olsztyn are related to the poor properties of the activated sludge. This becomes particularly evident in winter and spring, when the SVI exceeds 190 cm g (Figure 1). Bulked sludge has an adverse effect on