The descriptions below are examples of process & technology developments, process modification and innovations, based on data & findings gathered from in-service systems, works upgrades and project commissioning. 

Final settlement tanks are designed to settle sludge with a minimum settling characteristic, which will allow settling in a retention of between 2 to 4 hours. Exceeding the design limitations of the settlement tank causes poorer settling, increased width of the hindered zone and subsequent ejection of the finer sludge over the weir.

Designing and operating the first settler in the sequence shown above, deliberately outside the specification of a conventional settler results in the ejection of fine sludge, and retention of larger and more mature sludge bio-culture, with superior settling and respiratory characteristics. Perpetual recycling of the settlable sludge, results in sludge floc aggregates reaching a sludge age in excess of 28 days.

The second settler shown on the diagram above, is a dissolved air flotation settler (DAF), used to deal with fine bio-culture growth which will otherwise not settle in a conventional settler. The system primarily waste sludge from the DAF, as the sludge floated also contain broken up mature floc aggregate that can't be maintained by the conditions in the reactor.

Wastewater Treatment – Internal solids recirculation for Activated Sludge, maturing bio-culture size, shape, density and functionality beyond conventional sludge age.

Internal solids recirculation for activated sludge sytems. The process design innovation shown on these graphics, uses an internal settling device to retain larger, heavier and more mature sludge floc on the bases of their settling characteristics. Settled flocs are returned via the internal recirculation, back to the pre-process contact tank on a perpetual cycle, maturing the heavy floc beyond the 10 day sludge age of the conventional system, without affecting the MLSS value.

This image shows the bio-reactor and the pre-process contact tank in greater detail. The internal settler is mounted on the far end wall, underneath the reactor effluent weir. The settled sludge is gravity fed and recirculated back to the contact tank, fitted with vigorous convection mechanics. The pre-process chamber may be operated in anoxic, anaerobic or pre-aeration modes.

The internal settler device is mounted on the reactor wall, and is adjustable for height and angle to allow for performance optimisation. The settler creates a still zone under the weir and convection flow to assist the larger flocs to travel laterally and then downward with gravity. The smaller and finer pin-floc travel up and over the weir, for normal separation in the final settlement tank.

Repeatedly selecting the heaviest and largest floc grains in a perpetual cycle, will result in substantial improvement in settling characteristics, and the densely populated floc grains form large communities of bacteria for reduced carbon, ammonium, nitrate and phosphorous removal. The larger the grains become, the bigger the aerobic, anoxic and anaerobic zones throughout the floc community.

Cycling the bio-culture through the three zones, provide the Poly-phosphate Accumulating Organisms (PAOs) with the environmental conditions to compete with the aerobic bacteria for resources.

The three zones are best created with three distinct compartments, but the assets on sites are not always available, especially when the site was not designed to support BPR. Most sites have been constructed with a single compartment reactor.

To convert a process from a conventional system to an EBPR systems, additional tanks, zoning and mixing are needed. This may be achieved in a number of ways and for this case, we are considering a small tank system, with an additional tank installed upstream of the aeration tank.

On the schematic above, the additional tank is managed to be an anaerobic fermentation zone, with the RAS being returned to both the back end of the first tank, and the front end of the second tank (like in a conventional system). The RAS contain the Nitrate Electron Acceptors that may be utilised by the Aerobic bacteria for respiration during the process of Di-Nitrification. With the design as shown above, the zones AB, and O, are effectively anoxic zone, with high concentration of SVFAs available for the bacteria to switch metabolic pathways to fermentation. Most of the bulk species of bacteria in ASP systems are capable of switching facultatively to respire with anaerobic fermentation metabolic pathways.

Other aspects of this process design, are the flow through the process from left to right as displayed creating the end anoxic zone in zone AB. Solids are allowed to drop out of suspension and form a pile at the bottom of the tank, becoming more anaerobic toward the deeper layers due to anoxic respiration activity in the bio-culture. From the boundary area between A and AB, a method of mixing or internal re-circulation of solids is in place to re-suspend the solids and move them into the influent stream near the tank inlet.

 In zone O, there is no aeration to provide the convection for solids to rise up from the bottom, creating another anoxic zone in the blanket of sludge dropping out of suspension. Further along the end of zone O, the aeration starts to create mechanical convection lift for the sludge floc, and normal aerated conditions prevail.

“Forever chemicals”, Polyfluoroalkyl substances (PFAS), have become a growing concern for public health, as concentrations of PFAS chemicals have been accumulating in the environment for the last 75 years.

At the contamination level seen in drinking water sources, it would appear if the problem is benign, but PFAS has a tendency to accumulate in final fate locations in the environment, most notably food sources such as plants and animals.

Because of the low concentration of PFAS molecules in WWT discharge, targeting it for removal is very costly. More economical solutions would be using existing technology to remove PFAS with other pollutants such as pesticides and metabolites of medicine.

The constructed wetland below is designed with integrated low-pressure membranes that will reject the un-biodegradable molecules in the WWT effluent. The PFAS containing reject (in pink, 3) is periodically recycled with the loop at position (8), to be added to the incoming load. The plants in the wetland remove the PFAS with 40-60% efficiency, with the higher the concentration in the recirculating loop, the higher the mass removal from the system.

The wetland is fitted below the gravel media with a porous membrane (in green) to protect the PFAS rejecting membrane (in white). Water and ionic minerals will still pass the membrane and is drained through the bottom left (4), and FE (5).

BPR is a challenging process with detailed knowledge of biochemistry processes and micro-biology required by attending technical support personnel.

Recovery of the stored poly-phosphate takes place with the wasting of sludge, and hence PAOs through the WAS line, shown at point 9 on the graphic below.

The design shown below include several innovations specifically to optimise the process for BPR recovery in the polyphosphate containing biosolids removed from the FSTs.

The major design changes to a conventional BPR system are:

• Counter-flow and underflow bio-culture solids recycling

• Subsurface influent points to optimise process conditions

• Variable tank levels for volume and HRT adjustments

• Low level tank overflow systems

The physical design innovations are necessary to be able to manipulate the conditions to be most favourable for the Poly-phosphate Accumulating Organisms, POAs (4, 6, 8). The intricate counterflow of concentrated solids allow for efficient cycling of bio-culture solids between optimised aerobic, and optimised anaerobic conditions (3, 7, 10, 11, 12, 13, 14, 15). The process can also be adjusted by using sludge blankets and tank levels to extend and reduce the volume capacity of the anaerobic or anoxic zones, according to process requirements for optimisation of phosphate removal (11, 12, 13).

BPR rely on the principle that Poly-phosphate Accumulating Organisms (POAs) will remove ortho-phosphate from the water, and accumulate Poly-phosphate (PP) inside the cell bodies during aerobic/starvation conditions. When the bacteria are then cycled back to Anaerobic conditions with available VFAs & Acetate, the POAs use the stored PP to release energy (no O2 for respiration), and store a reduced carbon polymer alkanoate (PHA) for future starvation periods.

In the anaerobic zone, the POAs will use energy from stored PP to accumulate PHA (Poly-hydroxyalkanoate), and release PO4 phosphate in the bulk water.

In the anoxic zone, and in the presence of SVFAs, the POAs will use energy from stored PP, and H-Ac to accumulate PHA, and release phosphate.

In the aerobic zone and with SFVAs in short supply, the POAs will use energy from stored PHA to accumulate PP from PO4, and for cell growth (Accumulate POA biomass).