Composting of activated sludge in adiabatic reactor

Abstract

U današnje vrijeme porastom broja stanovnika te razvojem industrije globalno raste količina nastalih otpadnih voda koje je potrebno obraditi. Biološkom obradom otpadnih voda, koja je zbog svoje jednostavnosti i ekonomske isplativosti jedna od prihvatljivijih obrada, zaostaje aktivni mulj kojeg je potrebno zbrinuti na odgovarajući način. Danas postoje razni načini zbrinjavanja aktivnog mulja, poput mehaničkih, bioloških i fizikalnih procesa. Aktivni mulj je bogat organskom tvari te je zbog toga pogodan za kompostiranje, a produkt – kompost se može odložiti na poljoprivredno tlo ukoliko zadovoljava uvjete koji su propisani pravilnikom. U ovom radu istraživana je mogućnost zbrinjavanja aktivnog mulja procesom kompostiranja. U cilju dobivanja optimalne mješavine aktivnog mulja (AM) i biootpada (S) ispitani su različiti omjeri mješavine supstrata i aktivnog mulja (SP – biootpad, P1 – S/AM = 2,5:1 ; P2 – S/AM = 5:1 ; P3 – S/AM = 7:1) u reaktorima radnog volumena, Vr = 1 L. Proces kompostiranja u adijabatskom reaktoru radnog volumena Vr = 10 L (P4) proveden je s mješavinom koja je pokazala najbolje rezultate u pokusima koji su se provodili u manjem reaktorskom mjerilu (P1). Proces kompostiranja trajao je 16 dana te su praćeni sljedeći parametri: temperatura, ukupan broj mikroorganizama, C/N omjer, udio vlage, udio hlapive tvari, pH supstrata i kondenzata, volumen kondenzata,udio nastalog CO2 i NH3, koncentracija amonijevih iona i konverzija. U pokusima SP, P1, P2, P3 i P4 postignuta je konverzija od 39,81 %, 44,35 %, 49,72 %, 48,85 %, te 42,21 %. Ukupna koncentracija CO2 u pokusima SP, P1, P2, P3 i P4 iznosila je 644,72 g kgHT0^-1,660,13 g kgHT0^-1, 511,79 g kgHT0^-1, 565,38 g kgHT0^-1, te 344,42 g kgHT0^-1. Maksimalna temperatura u pokusima SP, P1, P2, P3 i P4 iznosila je 57,1 °C, 58,3 °C, 61,4 °C, 62,8 °C i 57,48 °C. Termofilna faza u pokusima SP, P1, P2, P3 i P4 trajala je 3, 13, 7, 5 i 4 dana.Today, with the increase in population and the development of industry, the amount of wastewater that needs to be treated is growing globally. The biological treatment of wastewater, which is one of the more acceptable treatments due to its simplicity and economic viability, legs behind the activated sludge that must be disposed appropriately. There are various ways of treating activated sludge, such as mechanical, biological and physical processes. Active sludge is rich in organic matter and therefore is suitable for composting, and the product – compost can be disposed on the agricultural soil if fulfill the conditions prescribed by the ordinance. The aim of this work was to examine the possibility of treatment of activated sludge by composting process. In order to obtain the optimal mixture of activated sludge (AM) and biowaste (S), different ratios (SP, P1, P2, P3) of substrate and activated sludge were tested (SP - biowaste, P1 - S / AM = 2.5: 1; P2 - S / AM = 5: 1; P3 - S / AM = 7: 1) in reactors with working volume of Vr = 1 L. The composting process in adiabatic reactor with working volume of Vr = 10 L (P4) was performed with the mixture that provided the best results in experiments conducted at a smaller reactor scale (P1). The composting process lasted 16 days and the following parameters were monitored: temperature, CFU, C/N ratio, moisture content, volatile matter content, substrate and condensate pH, condensate volume, CO2 and NH3 content, concentration of ammonium ion and conversion. In experiments SP, P1, P2, P3 and P4, a conversion of 39,81 %, 44,35 %, 49,72 %, 48,85 % and 42,21 % was achieved, respectively. Total CO2 concentration in experiments SP, P1, P2, P3 and P4 was 644,72 g kgVM0^-1,660,13 g kgVM0^-1, 511,79 g kgVM0^-1, 565,38 g kgVM0^-1 and 344,42 g kgVM^0-1, respectively. The maximum temperatures in SP, P1, P2, P3 and P4 experiments were 57,1 °C, 58,3 °C, 61,4 °C, 62,8 °C and 57,48 °C, respectively. The thermophilic phase in the SP, P1, P2, P3 and P4 experiments lasted 3, 13, 7, 5 and 4 days, respectively