Influence of wastewater treatment plants' operational conditions on activated sludge microbiological and morphological characteristics

Abstract

The effect of wastewater composition and operating conditions in activated sludge (AS) microbiological and morphological characteristics was studied in three AS wastewater treatment plants (WWTPs): (a) a high organic load slaughterhouse AS WWTP, operating at complete solids retention, monitored from its start-up and for 425 days; (b) a seasonally operational, low nitrogen load fruit canning industry AS WWTP, operating at complete solids retention, monitored from its start-up and until the end of the season (87 days); (c) a municipal AS WWTP, treating wastewater from a semi-combined sewer system, monitored during the transitions from dry to rainy and again to dry periods of operation. The sludge microbiological and morphological characteristics were correlated to nutrients' availability, solids retention time, hydraulic retention time, dissolved oxygen, mixed liquor suspended solids (MLVSS), organic load (F/M) and substrate utilization rate. The AS WWTPs' operation was distinguished in periods based on biomass growth phase, characterized by different biological and morphological characteristics and on operational conditions. An anoxic/aerobic selector minimizes the readily biodegradable compounds in influent, inhibiting filamentous growth. Plant performance controlling is presented in a logic flowchart in which operational parameters are linked to microbial manipulation, resulting in a useful tool for researchers and engineers.

Comparison of the Results from Microscopic Tests Concerning the Quality of Activated Sludge and Effluent

“…The authors have identified SBI as a very useful indicator for determining both the condition of activated sludge and the analysis of biological working conditions of treatment plants. Identification of micro-fauna in mixed wastewater (domestic and industrial) has been recognized as an important element by many researchers [22,[33][34][35][36].…”

Innovative Approach on Aerobic Activated Sludge Process towards more Sustainable Wastewater Treatment

“…Relative small deviations in influent measured characteristics were observed due to the use of an influent equalization tank ( Table 1). The mean COD:N:P ratio in influent was 150:9.8:1.8 (sufficient nutrient content), while the BOD20/COD and BODultimate/COD ratios were 0.91 and 0.98 respectively (highly biodegradable) [15,18].…”

“…The biomass of WWTP-1 is characterized by (a) the growth of metazoan such as rotifers, especially after reaching stabilization phase, (b) small biomass flocs and (c) good settling characteristics (SVI < 100) [21]. Filamentous species have never been observed in WWTP-1, probably due to the higher than 4 mg/L DO concentration in the aerobic stages and the use of the preliminary stage that acts as a microbial selector [13][14][15].…”

“…WWTP-1's innovative design [12] and operation is based on CRAS process and consists of a preliminary, simultaneous nitrification/denitrification treatment stage and a pre-anoxic denitrification, complete mix, extended aeration AS treatment stage with complete retention of solids. The effluent of the preliminary system, which acts as a microbial selector by utilizing readily biodegradable COD [13][14][15], overflows in the extended aeration system, while excess sludge is transferred periodically from preliminary stage into the extended aeration stage (Figure 1). Prodromos Pavlides SA's WWTP (WWTP-2) is located in Giannitsa Province of Pella Prefecture, Central Macedonia, Greece.…”

“…Each treatment line consists of (a) an aerobic treatment stage followed by sedimentation (preliminary treatment stage) and (b) secondary aerobic treatment stage followed again by sedimentation (secondary treatment stage). The preliminary treatment stage offers an initial COD removal, especially of the readily biodegradable substrate, thus it acts as a microbial selector [13][14][15]. The effluent from the preliminary stage's sedimentation tank inflows to the secondary treatment stage in order to further reduce it COD content.…”