Combination of Microscopic Tests of the Activated Sludge and Effluent Quality for More Efficient On-Site Treatment

Abstract

Container on-site wastewater treatment plants are systems of growing interest in the areas where sewer systems cannot be implemented. In this study, container on-site wastewater treatment plant with low-loaded activated sludge has been examined. The aim of the study was: (i) to assess the efficiency of the plant; and (ii) to evaluate the relationship between the condition of activated sludge and selected parameters of effluent quality. Effluent quality has been characterized by the reliability factor (RF) and technological purity index (TPI). Sludge quality assessment covered measurements of volume (Vo), dry matter (DM), sludge index (SI), and the unit oxygen consumption rate (UOCR). Microscopic analysis has been performed to assess the morphological (flocks) and biotic quality (sludge biotic index, SBI) of activated sludge. The research has been completed by an on-site measurement of dissolved oxygen concentration in an activated sludge chamber with 30 s intervals. Results confirmed a significant (p < 0.05) correlation (CC = −0.9277) between biochemical oxygen demand (BOD5) and SBI for the oxygen level in the aeration chamber between 1–2 mg/L. Negative significant correlation (p < 0.05) has also been found between SBI and electrical conductivity (EC) (CC = −0.7478). In the examined case, the optimal EC of the effluent was in the range of 600–800 µS/cm.