Biological wastewater treatment processes are economical and environmentally sustainable for the removal of organic pollutants from wastewater. The biological wastewater treatment processes are basically biochemical oxidation processes in which under controlled environmental conditions in the presence or absence of oxygen, micro-organisms utilise the organic matter for the production of energy by cellular respiration and for the synthesis of protein and other cellular components for the production of new cells. The process occurring in the presence of oxygen is termed as “Aerobic” process. The biological wastewater treatments processes can be further classified in two categories: 1) Suspended growth and 2) Attached growth or bio film processes. Moving Bed Bio-Reactor (MBBR) and Sequential Batch Reactor (SBR) are extensively used technologies at present in Wastewater Industry worldwide. Amit Christian, Area Manager, Greywater: Jaldhara Technologies, Ahmedabad Area, India initiated a discussion on the comparison of these two technologies on the basis of influent quality treated, effluent quality achieved, Foot print, Sludge production, Aeration Requirement, flexibility of operation, robustness against undesirable conditions (e.g. shock loadings, temperature variations & flow variations), operation & maintenance cost and capital cost, here are the excerpts of the discussion.
Based on the data provided, it indicates that apart from short retention time and higher throughput less foot print would be a distinct advantage of MBBR, as biomass yield and air requirements are quite similar to other processes. However, the F/M ratio seems to be quite higher. How well is MBBR performance for nutrient removal?
From microbial point of view, these two are completely different technologies – one being the suspended growth and the other being the fixed film technology. Let us assume that you have pure domestic waste generated from residential areas and you have to achieve Biochemical Oxygen Demand (BOD) or Chemical Oxygen Demand (COD) removal along with Biological Nutrient Removal (BNR). In this scenario how would you compare the above mentioned parameters?
Robin Schroeder, Environmental Specialist, Environmental Business Specialists, Mandeville, Louisiana
Having worked with SBR but not MBBR, SBR does have a small footprint, but relies heavily on pre-treatment equipment and equalization in order to run smoothly. All the extras end up creating a much larger footprint than the original concept. The influent quality must be maintained within a range (equalization), from what I have seen, to keep the system operating smoothly. Bumps in loading are quickly seen as turbidity in the effluent. The effluent quality can be very good, but the operation changes so rapidly that it requires a skilled operator to maintain a good effluent through the various cycles. According to my experience, the SBR does not handle shock loading or flow variations very well.
Dennis Hunter, CEO, EEC European Division, St John’s Innovation Centre Cambridge, UK
With MBBR the process is a continuous biofilm process in four stages with a specialized function with first being BOD removal, second – Nitrification third- De-nitrification and finally Clarification.
In order to provide efficient nitrification all soluble BOD’s must be burned out. This is provided for in a two reactor system, of which the second may be considered as a polishing reactor for BOD. This reactor is designed with a low specific BOD loading 4gr/m2/day. In normal cases Nitrification will start at this loading. Hence, the reactor may also be considered as a starter for the Nitrification Reactor.
The Nitrification is also provided for in a two reactor system, but in this case the second nitrification reactor will operate at a low DO level, 3mg/l, so that the following anoxic de-nitrification reactor may operate efficiently. About 2/3 of the ammonia is nitrified in the first reactor at a DO level about 6mg/l
The de-nitrification reactor comes as a single reactor and ensures that the N03-N requirement is met. There is also provision for pre-denitrification in the pump well by recirculation from the 2nd nitrification reactor, but this not counted for in the design.
Totally, the COD load on all aerated reactors is 12 gr. COD/m2/day, while the nitrogen load on the anoxic reactor is about 2 gr. N03-N/m2/day. MBBR systems are designed with a final clarifier in place, because the footprint is very small with the clarifier already included, compared with the other processes. There are no problems with ‘odour’ if the MBBR plant is operated correctly. As for sludge removal, it depends on whether the end user prefers to tanker away off-site, liquid sewage, at regular intervals, or to put in place a sludge management system. Often this is a financial decision.
Most HDPE media used in MBBR processes should be for at least 20 years. We use AMB bio media and this is the guaranteed lifetime. You will generally see MBBR process using one reactor for Membrane Treatment (Ultra Filtration) and this makes the whole process more affordable. Having said this, I can foresee that in the future, when the cost of Membrane Treatment will reduce, MBR will take over from MBBR.
Stuart McGowan, Director at Solent Technical Solutions Ltd, United Kingdom
To get a good quality effluent from an MBBR system final clarifiers are required. This increases the footprint significantly. SBRs can be constructed on very small footprints and can even double stacked as at Ringsend sewage works which serves Dublin in Ireland.
It would seem to me that SBR and MBBR systems have two inherent problems. The first is odour, and the second is sludge removal (collection, compacting and disposal). You might want to look at a new technology (Seair diffusion systems) utilizing ozone and oxygen at super saturation levels. In stage one (the collection tank) ozone immediately eliminates odour and it breaks down sludge into carbon and heat. In the second stage, super oxygenation (20-30ppm) reduces BOD and COD. In the third stage, ozone eliminates all bacteria meeting Canadian standards for recycling or ground disposal. The footprint is exceedingly small. For example, we have a complete wastewater treatment system next to the 13 Tee box at a local golf course.
Mahmoud Kabeel, Sales Manager, Metito Overseas Ltd., Riyadh, Saudi Arabia
We have developed with our partners, an advanced MBBR process which saves more than 60% of space & power consumption compared to conventional process. It has an edge over the SBR process as it is much more compact (less by 25% in foot print compared to the SBR) and the most advanced edge is that hardly any sludge is produced. It is an attached growth Biomass process called: Turbo4Bio.
For operating cost, it is 60% less than any process and in terms of capital cost it is also much more economical. There are no foul odours but the screening and FOG treatment must be well designed. There is no tertiary treatment required and you can reach less than 10 PPM BOD5/TSS by far. We are building currently a 50,000 m³/day plant using this technology. This is a revolution in Waste Water Treatment Industry!
In short, SBR and MBBR process cannot be combined. SBR process can accept fluctuating flows and it goes in the batch process, while MBBR needs a smooth consistent flow. It is simply an attached growth process. Such a combination can be used in case of high BOD/COD at the inlet, where MBBR process can be used in one of the stages.