The descriptions below are examples of process & technology cases, remediation projects and process assessments, based on data gathered from in-service systems, research and optimisation projects.

Understanding the functioning and process chemistry of a Nitrification-Denitrification process, and the technology settings to optimise the process is vital for effective technical support to the attending personnel operating the technology.

Although records of Nitrous Oxide emissions have been shown to be minimal, there are conditions in certain WWTw, where these emissions are unacceptably high. Let us look a bit closer at some of these conditions.

The attached graphic shows a activated sludge process designed with the approach of optimising de-nitrification in a dedicated anoxic zone, and minimising spontaneous anoxic-denitrification in the other anoxic & anaerobic zones that may exist in the bio-reactor or final settlement tanks.

The design shows the process with an additional tank before the bio-reactor, that can be used to optimise the de-nitrification. RAS is recycled into the Anoxic/Dilution tank, and there is an additional FE recirculation system to be used as a further part recirculation loop for nitrate. The anoxic tank is positioned to receive influent which has been subject to pre-acidification, to allow for the necessary levels of fermentation products to be available as a SVFA carbon source. 

The anoxic tank can handle solids trough the bottom to allow for the RAS to be efficiently returned to the main reactor after de-nitrification has been completed. The anoxic tank can be operated with a variable volume by emptying the flow through the bottom hopper with the solids. This aspect allows for flexibility for adjusting the HRT of the anoxic conditions to requirements, and to adjust the concentration of incoming ammonia before entering the main reactor, by part recirculating the FE. (Improved de-nitrification with high concentration)

Nitrous oxide emissions are known to become excessive when the enzymatic reduction processes of de-nitrification are incomplete, stressed or interrupted. This may happen when de-nitrification happen in the reactor and FST, when the dissolved oxygen is low (high carbon load, high concentration NH4, inadequate DO & aeration capacity), when there are not enough SVFAs available (late in the lane and in the FST), and when the alkalinity of the system is to low. 

The data shown on the image below is from a process assessment done on two lanes of an Air Activated Sludge system, with different settings, efficiency and performance outcomes.

The two lanes were identical sized and fed from the same PST, with different MLSS concentration, aeration settings and return RAS rates.

The data show the measured DO values, and BOD and NH4 concentrations down the lane. Lane B, was recently adjusted to operate with 2/3 of the MLSS concentration of Lane A, and a higher RAS rate to compensate for the loss in F:M ratio, in order to achieve better aeration efficiency.

With the adjustment, the outcomes for BOD and NH4 were negative, and lane B consistently breached the 80% limit for the discharge quality. The graphic shows the measurements of BOD, NH4 and SS down the length of the lane, and is a fitted curve from 6 equal distance, individual measuring points.

In lane B, the BOD & NH4 concentration stayed higher for a considerably longer distance down the lane, and both concentration values were consistently close to the 100% breach level at the end of the lane, despite DO measurements being higher in lane B, and air consumption being reduced by a fair amount, compared to Lane A.

For lane B, the solution was to change the FST settings to concentrate the RAS, and reduce the RAS rate. This lengthened the HRT and therefore extended the reaction time for both bio-chemical reactions for BOD and NH4. After two days of operation with the new settings, the Lane B was achieving better results for discharge than Lane A, with substantially improved air consumption efficiency.

With remote SCADA systems installed on most modern wastewater treatment systems, remote monitoring has become a key necessity to provide effective technical support to personnel attending the process.

Online data recorded by SCADA systems or remote monitoring instrumentation are stored in data bases, accessible remotely and updated in real time or sometimes with an hour or two delay. 

The interval data records can be downloaded in data management software like Microsoft Excel, and consolidated into one data record, correlated with manually recorded data from routine monitoring, environmental sampling and measurements during specific events, exceptions or failures.

Routine tasks during process operations and management require accurate data processing, and valuable tools that familiar to almost everyone, are pre-programmed process calculators on Microsoft Excel.

These calculators can be prepared for quick and accurate calculations for process measurements, process technology settings and process design verification. Processing data manually before entering the data on the database may lead to errors creeping in from time to time.

Designing robust, stand-alone calculators, with large input fields and low corruptibility, for measurement recordings is vital tools to process data accurately. Calculators may also be programmed with instant feedback warnings for the results and indicators when the results have possibly been entered incorrectly.

Understanding the functioning and bio-process chemistry of a Secondary Treatment process, and the technology settings to optimise the process is vital for effective technical support to the attending personnel operating the technology.

Biochemical Oxygen Demand is the key management parameter for treatment systems that utilise bio-technology

Oxygen demand in a wastewater treatment system describes the measurement of dissolved oxygen uptake by the concentrated bio culture from the water, to use as electron acceptors during metabolic processes. The measurements can be made with normal dissolved oxygen sensors, and the BOD value recorded after a time period, is called the equivalent mass of oxygen, need to convert reduced carbon to carbon dioxide, and reduced nitrogen to nitrate. In simple terms this means dissolved oxygen uptake is measured as a mass, to establish the equivalent mass of biodegradable molecules, like fatty acids and ammonium, that is being consumed by the bio culture.

BOD is measured by measuring the start DO in a sample with a known content of bioculture. After a period of time, the end DO is measured. The difference in DO, start value, minus end value, is the BOD of that sample for the time it was measured in. The three graph plots shown here were created using data measured every six hours, for samples S1, S2 and S3, all with the same culture dilution, but different levels of biodegradable carbon added. Meaningful measurements for BOD may be taken at any point along the curve, and allowing the test to progress until oxygen uptake terminates give the value of ultimate BOD.

The special case of BOD five, a BOD measurement performed to an international standard, ISO 5815/1, or ASTMD 6238, is a widely used BOD measurement to measure biodegradable carbon pollutants in water. The measurement is completed in 5 days and the standard describe performing the test to very strict guidelines for dilution, culture seed, temperature and attenuation of unwanted reactions, such as DO consumption from ammonium. cBOD five is the measurement included and measured for in environmental permits for discharge regulation.

This is data recorded for a BOD test, showing the recorded DO values and calculations to develop usable parameters for process modelling. The data was processed with excel, and the formula for the fitted curve provides an easy way to model the BOD data from an earlier point on the calibrated curve.

BOD measurements are very accurate predictors of the bio-availability of nutrient substances in the feed. Substances like short and medium chain fatty acids, sugars, amino acids, ketones and organic acids are dissolved substances that will accelerate bio-culture metabolism instantly, exerting an increased oxygen demand on the process.

A BOD analysis of the feed sample will provide information with regards the food to biomass ratio (F:M), that allow the process personnel to adjust the MLSS concentration to maintain healthy bio-culture. The F:M ratio that is suitable for your process depends on your BOD test, and process and is best determined by experimentation. Using a BOD analysis for this instead of a COD analysis is much more reliable as the COD analysis give a false reading with the varying degree of inert organic material being measured with the biodegradable organics.

Understanding the composition of raw influent and the impact that the different fractions carried by the wastewater have on the bio-technology, the process performance and the settings to use for the process, is vital for effective technical support to the attending personnel operating the technology.

Wastewater Treatment influent composition, measuring the different constituents and considering their fate and method of removal, by an activated sludge system. In this section, we also look at the effective mass measurements we may use to determine the pollution load on the treatment system.

Let us consider a sample collected from the crude influent or settled crude, from a position after the primary treatment processes. The sample contains pollutants that include silica, sand, food particles, faeces, toilet paper, plant and animal waste, and organic molecules from medicines, food additives and industrial waste. All the constituents are dispersed through the sample volume, and are either dissolved, suspended or colloidal suspended.  The wastewater pollutant load may be measured at this point with tests like, total solids, total suspended solids, chemical oxygen demand, COD, biochemical oxygen demand, BOD, Total organic carbon, TOC, or total volatile solids. Each of these measurements may give us a clue as to the overall composition of the sample pollution load, and how the activated sludge system is going to respond to the different fractions of pollutants.

Let’s summarise the discernible fractions that we are considering. On the left we can see the totally dispersed sample that contain all the fractions. In the middle we can see the sample settled, with the supernatant volume at the top. On the right the coloured bands represent the mass fractions, determinable by mass measurements of the different analysis methods we have discussed. For reference the fractions are marked with the acronyms corresponding to the coloured band as displayed.

For the supernatant fraction, the most valuable data would be the Biochemical Oxygen Demand. The dissolved fraction of BOD is by far the most important load fraction for the activated sludge process, as most all the immediate nutrients for the bio-culture to respire with, are carried as dissolved bio-degradable organic molecules. These nutrients would be reduced carbon as sugars, carbohydrates, short, medium and long chain fatty acids, amino acids and proteins. 

Reduced nitrogen compounds are also a food nutrient for the bio-culture as ammonium and urea are present often in high quantities of above 50mg/L. Micro nutrients as magnesium, calcium, potassium and bicarbonate are also in the dissolved fraction, but considered as the inert mineral constituents vital for bio-culture health. Of the inert mineral micro nutrients, measuring for alkalinity should also be done regularly, or online monitoring if the process is located in a soft water catchment.

Looking at the dissolved biodegradable substance load in the previous section, it is obvious that some common oversights from the last century, are still with us today. Contrary to what are still being taught in wastewater texts and academic courses, the rates of diffusion of dissolved substances, food nutrients and micro nutrients have a significant impact on activated sludge bio-culture health, and the systems performance as a whole. Understanding the model for Fick’s second law of diffusion goes a long way in understanding that the dissolve biodegradable fraction that carry the bio-culture nutrients, diffuse at a much faster rate than any of the other constituents. 

The reason for this is that the nutrients are being consumed and converted along the pathway of dX. Refer the model on the diagram. This means that the second derivative against time, dT needs to be considered. The concentration gradient for the biodegradable organic nutrients increases dramatically, and hence their rate of diffusion to the internal metabolic centres inside the bio-culture. The significance of this accentuates the importance of using a process indicator, such as the BOD measurement for the supernatant fraction, as a measure for the F to M ratio.

The information on the accompanying diagram shows the positions commonly used for regulatory monitoring and management measurements

I-Inlet, regulator monitoring for Flow Vi COD, NH3, Suspended Solids

1 – measurements Flow Vi, COD, BOD, TS, SS, NH4

2 – measurements COD, BOD, TS, SS, NH4 (1-2 for PST performance)

P – measurements COD, BOD, TS, SS, NH4 (individual PST performance)

A, 3 – measurements NO3, NH4 (3-4 Anoxic zone performance)

4 – measurements Flow VR COD, BOD, PO4 NO3, NH4 (Reactor performance, settings)

5,6,7, L1, L2, L3 – measurements DO, BOD, NO3, NH4 (3-4 Anoxic zone performance)

7 – measurements MLSS, BOD, PO4 NO3, NH4 (Reactor performance, settings)

8 – measurements for RAS concentration, flow Vr

9 – measurements for WAS concentration, flow Vw

F, E – measurements for SS (7-E FST individual performance)

10 – regulator monitoring for all permitted parameters, Flow Vi COD, BOD, NH3, SS, PO4 NO3

Initial learning session 01, further includes the measurement and analytic methods for all the parameters as described above, including practical activity breaks for sampling and laboratory skills practise.