Rural Water - Quarter 3, 2017 - 39
BY MICHAEL CHERNIAK, SENIOR VICE PRESIDENT, WOODARD & CURRAN, INC.
Some substances may inhibit
respiration, slow growth rates, damage cell
walls, change flocculation characteristics
or simply kill susceptible microbes. Low to
moderate levels (≤ 10 ppm) of chromium,
copper, zinc, surfactants and quaternary
disinfectants promote stress and inhibition.
Strong oxidants such as peracetic acid
may cause complete cell destruction.
Combinations of inhibitory substances may
express antagonistic impacts at otherwise
"low" concentrations of those substances.
The following represent the most
common and significant sources of biological
inhibition and/or toxicity:
* Effluent BOD and TSS values begin to rise
above their moving averages
* Effluent ammonia levels gradually or
suddenly increase over 1.0 mg/L
* A sudden rise in dissolved oxygen i.e.,
two times the typical operating level
or an increase to levels > 5.0 mg/L
could indicate no microbial O2 demand
* Treated effluent COD removal begins to
fall below 90%
* Settleometer tests reflect floc
deterioration - poor settling, poor
compaction or deflocculation
* Settleometer supernatant becomes
turbid, milky, amber or darker tea shades
* Microscopic observations indicate lack of
movement by ciliates and rotifers
* Large numbers of flagellate microbes
begin to appear or dominate
Once a system shows signs of
inhibition, toxicity or non-compliance,
begin to diagnose the biomass health,
identify potential causes and implement
recovery. Also, begin to document available
information to validate toxicity suspicions.
1. Take some immediate pictures of affected
unit processes - influent waste, effluent
Characteristics of healthy biomass
quality, clarifiers, process foams, aeration
tanks. Snap settleometer photos of
characteristics and supernatant quality. If
possible, take pics of microscopic slides.
Review process control data and log
book entries. Use SCADA trending
abilities to graph flows, pH, aeration tank
DOs, blower run info, chemical feeds and
effluent quality. Trend whatever available
data helps tell a story.
Determine if the effluent quality is
meeting permit discharge limits. Consider
the ability of all discharge options to
accept sub-standard effluent. Is there an
impact on reclaimed water, surface water,
or spray-fields? Can flow be temporarily
diverted to off-line empty tanks or ponds?
Determine if toxics are still entering
the WWTP. Identify potential sources.
Consider in-plant activities such as
unusual dewatering sidestreams,
tanks/sump drains, chemical spills or
Analyze the effluent for pH, ammonia,
nitrate, TSS and COD. Compare results
to permit limits. Sample and test the
influent wastewater for pH, alkalinity,
COD and nutrients.
Surfactant and emulsion stream at lift station
6. Assess biomass (MLSS) viability.
Run settleometer SSV5, SSV30 and
supernatant turbidities. Also, run nutrient
analyses - ammonia, nitrate, nitrite and
orthophosphate. Compare results to
7. Oxygen uptake rate tests may be helpful
in biomass assessment and recovery
monitoring. The OUR result of a dead
biomass is normally zero and gradually
increases as bacteria return. The OUR
demand will increase substantially after
seed sludge is added - provided that the
toxic material has been neutralized or
removed from the system. OUR testing
requires a properly calibrated DO meter,
BOD bottle and probe, magnetic stirrer
and timer. A series of OURs using the
RAS is better described in any one of
a number of wastewater laboratory,
process or control manuals.
Should all observations conclude that
biomass damage or non-compliance has
occurred, consider the following:
1. Assure that the aeration system is
supplying as much dissolved oxygen
as possible (greater than 2.0 mg/L).
Continue until effluent ammonia testing