An Integrated Approach to Lysis-Cryptic Growth (Sludge Ozonation) and Sequencing Batch Reactor Coupled to an Anaerobic Side-Stream Reactor (SBR-ASSR): Performance and Characteristics

ABSTRACT

Anaerobic side-stream reactors (ASSR) have been suggested to reduce waste activated sludge volumes benefiting from relatively low capital/operation costs and design simplicity. In this study, an evaluation of the feasibility of combining the ASSR system with the lysis-cryptic growth (ozonation) process was made so that a part of the sludge which passed through the ASSR anaerobic tank would be then treated by ozonation before returned to the aeration tank. The main independent factor was the ozonation flowrate (OFR), which is defined as the percent of return sludge which passed through the both the anaerobic tank and the ozonation unit. Three systems were studied, an ASSR control without ozonation (OFR-0), a combined ASSR with ozonation designated as OFR-2.5 (anaerobic interchange rate [AIR] of 10% per day and 25% of the exchanged sludge being ozonated [ozone interchange rate or OIR]), and OFR-3.1 (AIR = 12.5%, OIR = 25%). The results revealed that the insertion of an ozonation step led to an enhanced total microbial activity, eukaryotic population, and nitrogen removal. The linear relationship between the observed yield and the specific oxygen uptake rate indicated that microbial predation was the major relevant mechanism for the enhanced sludge reduction. The results of measurements of particle size distribution, and sludge dewaterability rates suggest that additional studies are needed to better understand and optimize this system.

Graphical Abstract

KEYWORDS:

• Excess sludge reduction
• anaerobic side-stream reactor
• ozonation
• microbial predation
• extracellular polymeric substances
• microbial activity

List of abbreviations

ASSR Anaerobic side-stream reactor

AIR Anaerobic interchange rate

OIR Ozonation interchange rate

OFR Ozonation flowrate

SOUR Specific oxygen uptake rate

SCOD Soluble chemical oxygen demand

Y_obs Sludge observed yield

HRT Hydraulic retention time

EPS Extracellular polymeric substances

LB-EPS Loosely bound Extracellular polymeric substances

TB-EPS Tightly bound Extracellular polymeric substances

SRF Specific resistance to filtration

PSD Particle size distribution

dp Cumulative percent

Article highlights

• 1- Various sludge ozonation flowrates (OFRs) were investigated through a combination system between ASSR and ozonation unit.

• 2- Partial ozonation let to enhance autotrophs and heterotrophs activity within aeration tank of ASSR system.

• 3- Application of ozonation system caused the enhancing of microbial predationmechanism in ASSR system.

• 4- LB-EPS was the major factor to deteriorate sludge dewaterability whereas a relatively increase in sludge particle sizes was observed.