FAQ's
Frequently Asked Questions
The below questions have been collated from interested parties:
SMART units look similar to conventional RBCs. What are the main differences between the HYBACS process and RBC?
SMART units are similar in mechanical aspects to RBC units. However, whereas RBC units have contactor discs made from solid material, SMART units have discs made from a highly porous three-dimensional reticulated mesh comprising strands of plastic fibre. The mesh, which is 40 mm thick, gives SMART units a much higher treatment capacity per unit disc area and per unit volume of reactor. The mesh discs, drive shaft and driving gear of the units are robust and durable.
Does the HYBACS process require continuous dosing of Bacillus bacteria?
The HYBACS process grows its own sustained population of Bacilli and does not require any dosing of imported Bacillus, apart from the initial seeding using surplus sludge (or cake from another HYBACS treatment works). The design and operation of the HYBACS Process ensures a large and stable population of Bacilli in the biomass.
The performance of conventional activated sludge plants may be enhanced by dosing Bacillus spores purchased from suppliers. However, unless the treatment works are designed and operated to encourage the growth of Bacilli, they quickly wash-out from the biological system, so that period dosing is necessary to maintain their population.
What are the Operating & Maintenance expenses in comparison to the Conventional A/S process?
The major OPEX savings offered by the HYBACS Process compared to conventional activated sludge for example is in the reduced power consumption, as indicated in A4.
Provided the wastewater is adequately screened using 10 mm (or less) apertures, SMART units require no maintenance apart from the cleaning of the plates which may be needed at intervals of six months or more. Such cleaning is carried out in-situ using a pressured water lance.
How does the HYBACS process achieve up to 50% energy reduction?
The HYBACS Process saves energy because the first stage, containing the SMART units, removes approximately 50% of the BOD from the wastewater and much of the nitrogen, but consumes comparatively little energy because the aeration is achieved by the rotating discs. The following table compares the average energy consumption rates of a generic activated sludge plant (such as an A2/O plant) with a HYBACS plant; both plants are designed to remove TN and TP as well as carbonaceous matter. In this example, power consumption in the HYBACS process is 61% of the consumption in the activated sludge plant.
| Parameter | unit |
Generic activated sludge |
HYBACS |
|---|---|---|---|
| Population equivalent | PE (000) |
100 |
100 |
| Flow and Loads | |||
| Average flow rate of wastewater | m3/day | 24000 | 24000 |
| Maximum hourly-average flow rate of wastewater | m3/day | 54000 | 54000 |
| Average BOD load in settled wastewater | kg/day | 4200 | 4200 |
| Average TN load in settled wastewater | kg/day | 1011 | 1011 |
| Average TP load in settled wastewater | kg/day | 248 | 248 |
| Sizes of tanks | |||
| Volume of anaerobic zone | m3 | 2000 | 0 |
| Volume of anoxic zones | m3 | 4307 | 0 |
| Volume of aerated zones | m3 | 11200 | 5 600 |
| Number of SMART units | Nr | 0 | 22 |
| Plan area of clarifiers | m2 | 2 250 | 2 250 |
| Power Requirements for Secondary Treatment | |||
| Average mixing power in anaerobic zones | kW | 14 | 0 |
| Average mixing power in anoxic zones | kW | 30 | 0 |
| Average ancillary mixing power in downstream aeration zone | kW | 20 | 20 |
| Average power consumed by SMART units | kW | 0 | 35 |
| Average power consumed by aeration system | kW | 127 | 55 |
| Average consumed by clarification tanks | kW | 2 | 2 |
| Average power consumed by internal recycle pumps | kW | 10 | 5 |
| Average power consumed by external recycle pumps | kW | 11 | 13 |
| Total power for secondary treatment | kW | 214 | 130 |
| Specific energy in relation to wastewater flow | kJ/m3 | 642 | 390 |
| Specific energy in relation to BOD load | kJ/kg BOD | 4402 | 2676 |
How does the Phosphorus removal process operate and how it is possible to avoid the P release in the anaerobic sludge process?
Enhanced (or ‘luxury’) uptake of nitrogen occurs. The mechanism probably involves genera from the β-Proteobacteria class since such genera are known to accumulate phosphorus and are present in significant numbers in the biomass. It is also considered that Bacilli play a part in P removal but the mechanism is not known.
Data from HYBACS operational plants have demonstrated that average phosphorus removals of between 70% and 80% are obtained from wastewaters with TP/BOD ratios of up to about 4.0 w/w%. At the present time, the HYBACS process has not been tested on wastewaters containing higher TP/BOD ratios.
It is expected that the destruction of sludge solids in digestion tanks will release P, as in conventional activated sludge treatment and dosing of chemicals will be needed to precipitate the P.
In which circumstances are micronutrients required?
As for all biological treatment systems, the biomass in HYBACS systems requires a wide range of macronutrients and micronutrients. However, HYBACS biomass requires comparatively high concentrations of Mg+ + (a macronutrient) and SiO4- - (a micronutrient). There may be a need to dose one or both of these particular nutrients where concentrated wastewaters such as leachate, cess and some industrial wastewaters are treated, in circumstances where the wastewater is deficient in trace nutrients. Most domestic sewage contains both nutrients in sufficient concentration for the HYBACS Process. When nutrients are required, the required amount is dosed can be dosed as a powder. This lowcost consumable can be obtained from Bluewater Bio or independently.
What is the sludge production in the HYBACS compared to the A/S?
The HYBACS Process is considered to have a slightly lower sludge solids production rate compared with the activated sludge process. However, the HYBACS process can readily treat unsettled sewage, which reduces the sludge solids production rate by eliminating the production of primary sludge solids.
What are the characteristics of the sludge for thickening and dewatering processes, compared to activated sludge?
The sludge produced by the HYBACS process has much better settling characteristics than sludge produced by activated sludge plants, which results in treated effluents having comparatively low BOD and SS concentrations. HYBACS plants achieve treated effluents with BOD values less than 10 mg/l (expressed as a maximum) when treating municipal sewage. Further, activated sludge in HYBACS plants has not been known to ‘bulk’.
The activated sludge produced by HYBACS plants in Korea is readily dewatered using centrifuges into cakes with solids concentrations of 18 w/w% to 19 w/w%.
Are all the remaining parts of a HYBACS works similar to those in an activated sludge works?
The designs of ancillary processes for HYBACS plants are the same as for conventional activated sludge plants. However, because the HYBACS process produces a higher quality treated effluent, the use of HYBACS may eliminate the need for tertiary treatment in some circumstances.
Screening apertures at the head of the works need to be 10 mm or less, as indicated in A3.
Why is HYBACS a largely odour-free wastewater treatment process?
Under aerobic conditions, certain Bacilli species oxidise hydrogen sulphide and organic sulphides (mercaptans) to elemental sulphur. Such oxidation occurs primarily in the SMART units.
As a result of this oxidation, the SMART units substantially reduce the odour potential of the treatment stream. At some of the South Korea sites, prior to upgrading to the HYBACS process, there had been a history of complaints from local residents (see following photo illustrating proximity below). After the upgrading, there were no further complaints.
Considering the variability of wastewater quality, how can the predominance of Bacillus bacteria be guaranteed?
Bacilli are extremely versatile in their consumption of polluting matter. Existing treatment works using the HYBACS process are treating a wide range of wastewaters including domestic sewage, dairy waste, meat processing waste and leachate. Experience shows that the process readily handles short term (hourly and daily) variations in the strength and nature of the wastewater.
The process has a greater capacity to destroy pathogenic bacteria but could this bactericidal capacity also reduce treatment capacity?
All secondary treatment processes reduce the concentration of pathogens in wastewater, and enteric bacteria such as faecal coliforms are used to quantify such reduction. The HYBACS process has been shown to give an enhanced destruction of E. coli because Bacilli produce antibiotics which can destroy these and probably other pathogens.
There is no evidence that the antibiotics produced by Bacilli reduce overall HYBACS treatment performance in relation to the removal of carbonaceous matter, nitrogen and phosphorus. On the contrary, the HYBACS process produces very high quality effluents, reducing the BOD of concentrated wastewaters by 99% and producing effluents with BOD values of less than 10 mg/l from domestic sewage.
What are the changes/adaptations need to be made to an existing activated sludge plant for a HYBACS upgrade?
HYBACS can readily be used to upgrade existing activated sludge plants; indeed this is one of its strengths. In such upgrading, the SMART units are hydraulically placed between the primary sedimentation tanks and the existing aeration tanks. Generally, the size of aeration tanks designed for carbon-removal activated sludge plants is appropriate for HYBACS so that activated sludge works can be upgraded without any significant civil construction.
At treatment works where additional aeration volume is required for an upgrade, existing primary sedimentation tanks may be converted into aeration tanks and the SMART units placed upstream of the converted tanks.
Some changes may be needed to existing aeration tanks particularly with respect to partitioning and the distribution of aeration diffusers.
When is primary treatment needed?
The HYBACS process does not need primary sedimentation. Indeed, the process works better when the concentration of the wastewater is comparatively high. At treatment works where primary sedimentation is not installed, the production rate of sludge solids is reduced by some 30% but, of course, the consumption of electricity by the aeration system is increase by a similar proportion. Note that the aeration cost in a HYBACS plant is only about 60% of the aeration cost of an activated sludge plant treating the same influent to a similar standard.
In relation to nitrogen removal, what levels of performance can be expected?
The amount of nitrogen that can be removed from wastewater depends on the BOD/TN ratio of the wastewater. Where this ratio is greater than about 8, as found in some industrial wastewaters, HYBACS removes more than 90% of the TN from the wastewater. For municipal wastewaters for which the BOD/TN ratio is typically equal to 5, the removal of nitrogen is lower but the TN concentration of the treated effluent can still be made compliant with the European Waste Water Treatment Directive.
Nitrogen removal from landfill leachate containing BOD/TN ratios around 1.0 has been shown to be unusually high, averaging 94.9%. It is considered that the anammox reaction, occurring within the biomass of the SMART units, probably contributes to nitrogen removal under these particular conditions.
How stable is the biomass in the HYBACS process and under what range of conditions?
Provided treatment works are appropriately operated, HYBACS’ biomass is extremely stable in relation to its treatment capacity and can treat varying loads. Operational and maintenance requirements are similar to those required for conventional activated sludge treatment works.
An advantage of HYBACS over activated sludge is that the biomass has consistent excellent settling characteristics, so that high quality effluents are obtained consistently.
Should a treatment works have to be shut-down in an emergency, the biomass can be readily reinstated because, under the emergency conditions, the Bacilli cells form spores which then germinate when the wastewater supply and aeration are restarted.
Does Bluewater Bio provide treatment guarantees?
Bluewater Bio will provide treatment guarantees. Some applications will require pilot work to demonstrate performance and optimise operating conditions.
What is the quantity, quality and treatability of the sludge produced?
As explained previously, HYBACS sludge has superior settling characteristics to conventional activated sludge. In the Far East, most of the HYBACS plants function without primary sedimentation and the secondary sludge is centrifuged into cake for offsite disposal. The DS concentration of the cake is typically 19 w/w% which is comparatively high for cake comprising secondary sludge only.
Sludge (DS) production rate of the HYBACS process is considered to be slightly less than that for the activated sludge process.
What are the capital and operational costs in establishing and running a HYBACS plant?
Bluewater Bio is confident that HYBACS is more costeffective in terms of both CAPEX and OPEX than an activated sludge plant treating the same influent to a similar standard. HYBACS is also cost-effective for upgrading existing activated sludge works, especially where footprint is an issue. Bluewater Bio believes the treatment will also prove cost-effective in many instances against other technology families.
As explained previously, power consumption of the HYBACS process is 60% of that of an activated sludge plant producing an effluent of similar quality.
