PTQ Q1 2024 Issue

compaction, internal and external toxicity, reduced nitrifica - tion rates, and reduced COD removal rates. Holistic monitoring Predicting and addressing stressed conditions on a com- plex and dynamic system such as a refinery’s wastewater plant requires the implementation of a holistic monitoring strategy. The strategy should prioritise areas found to be most vulnerable for a given system, which should not be assumed to be the same as another wastewater system. For example, a wastewater system with limited secondary system capacity may need to focus on ensuring fast COD oxidation and rapid settling sludge, which may need to be enhanced with bioaugmentation and chemical aids. Closely monitoring the bioaugmentation and chemical systems will be important in this case. A system with adequate secondary system capacity but limited primary system capacity may be better served by honing in on monitoring for source control, primary chemical treatment programmes, and optimisation of the primary system. Once vulnerabilities are understood, set up a programme to monitor each wastewater asset. Some typical monitored parameters are found in Table 1 . Monitoring of primary treatment operations should include, at minimum, oil and grease (O&G), total suspended solids (TSS), COD, and turbidity. In addition to the influent and effluent of the primary treatment assets, other streams that should be monitored are specific influent streams (desalter brine), equalisation systems, API systems, floata - tion, and clarifier systems. Secondary biological treatment is the heart of most complex wastewater treatment plants, so a holistic moni - toring programme becomes ever more important as to the sensitivity and criticality of the process. Standard chemi- cal tests combined with dissolved oxygen uptake (DOUR), microscopy, and advanced tools such as Veolia’s BioHealth Adenosine Triphosphate (ATP) can provide unique insights to better understand the condition of the secondary sys- tem’s biology ahead of performance showing decline. BioHealth DNA genomics testing can also help detect shifts in the microbiome due to changes in food source or other stressors, enabling better long-term process decisions. Because BioHealth ATP testing considers multiple intrant factors to simulate the impact on the secondary treatment biomass, it can provide earlier detection of potential upset

conditions than other monitoring tools. Key output informa- tion includes Biological Stress Index (BSI), Active Biomass Ratio (ABR), Active Volatile Suspended Solids (AVSS), and True Food to Mass ratio (True F:M). BSI provides the ratio of ATP released from deteriorating cell membranes compared to the total quantity of ATP in a sample, which is a good indicator that inhibitory conditions are present. This allows operators to make smart decisions when considering discretionary loads and can help direct efforts in searching upstream for problematic flows and detrimental environmental conditions such as elevated temperature. ABR informs us how much of the system mass is actively doing the job of reducing contaminants. This information can help optimise plant operation and reduce excess energy consumption as it can be used to reduce the quantity of inert solids safely. AVSS gives the concentration of living biomass in the system. Each system has a specific range of AVSS that provides optimal performance, so once this optimal range is understood, deviation from the optimum should drive process control adjustments. AVSS can also be used to calculate food to mass (F:M) ratio. Traditional F:M includes comparing the mass of BOD to the mass of Mixed Liquor Suspended Solids (MLVSS), but replacing the MLVSS with AVSS provides more accurate information based on the amount of biomass that consumes nutrients. Monitoring the final stage of solids separation following the primary and secondary treatments is also needed to ensure a consistent operation that does not suffer poor efflu - ent quality. Clarifiers, which are most commonly used for removing remaining suspended solids, require a minimum daily record of settling rates, bed depths, solids concentra- tions, and overflow quality in order to adjust and optimise effluent quality. Operation strategy Data collected from the monitoring programme at the var- ious stages of the wastewater treatment process is key to making process control decisions. However, the basics should not be neglected, which apply no matter what the crude diet. The basics include:  Understanding your plant’s specific vulnerabilities  Understanding problematic substances from each process

stream and avoid shock loads to these streams  Communicating frequently with process units  Maintaining all equipment (maintenance fre- quency needs to increase with extra loading)  Optimising all primary treatment assets to remove as much insoluble matter as possible to protect downstream biomass  Optimising secondary treatment by giving the biomass a healthy living environment free from fast changes  Optimising clarification/solids separation. Primary treatment systems’ data should lead to operational decisions to prevent the process from becoming overloaded with excess solids and hydrocarbons associated with varying crudes’

Some typical monitored parameters when setting up a programme to monitor each wastewater asset

Primary effluent

Bio-reactor

Clarifier

Flow

MLSS, MLVSS, AVSS BioHealth ABR & BSI

Bed depth

SSV₅, SSV₃₀, SVI

TOC, COD, BOD

RAS flow RAS TSS WAS flow WAS TSS

TN, NH₃

DOUR, SOUR

TSS

F:M ratio

Oil & grease

Metals

Temperature Microscopy Biohealth DNA

Visual – scum, overflow

Known toxins

Turbidity

Alkalinity

Regulated parameters

Table 1

PTQ Q1 2024