Dear Hidayah,

There seems to be some confusion because all substances that you indicate or organic ones (assuming that LMW means Large Molecular Weight substances).

Please also clarify the term HPSEC.

Biological nitrification is an autotrophic process that oxidizes ammonia (NH4+) via nitrite (NO2-) up to nitrate (NO3+). In other words, no organics are involved in nitrification.

Could you be more specific about what kind building blocks; LMV acid ; neutral; SMPs and EPS please?

Dear Hidayah, find the following articles

1-Recent advances in membrane bioreactors (MBRs): Membrane fouling and membrane material.

2-Formation and quantification of soluble microbial products and N2O production by ammonia-oxidizing bacteria (AOB)-enriched activated sludge.

3-Modelling nitrification, heterotrophic growth and predation in activated sludge.

4-Morphological visualization, componential characterization and microbiological identification of membrane fouling in membrane bioreactors (MBRs).

5. A review of soluble microbial products (SMP) in wastewater treatment systems.

Nitrification involves the oxidation of ammonia to nitrite and nitrite to nitrate by autotrophic bacteria (i.e. those that fix CO2 rather than assimilate pre-formed organic carbon, which is what heterotrophs do). However, in a wastewater treatment process, other microorganisms will grow, depending on what is contained in the water treated by that process. For example, we found that an expanded bed biofilm reactor designed for tertiary nitrification also removed 62% suspended solids and 56% soluble CBOD. But we did not fractionate the organic matter.

Humic substances are extremely resistant to microbial attack, that's why a good soil is so full of them. So I wouldn't expect a conventional biological wastewater treatment process to remove them!

Nitrification will remove only organic material that contain ammonia or nitrite. Amino acids, imido acids could be removed during this process. As long as their is a nitrogen gropup in the LMW acids, nitrification can help. LMW acid w/o a nitrogen gropu will not respond. The same applies to SMPs also.

Sorry Chintha but once again - as meanwhile confirmed by Mike - nitrification is an autotrophic process starting with ammonia (NH4+). The degradation of organic nitrogenous compounds resulting in H2O, CO2, NH4+, ... is done by heterotrophs.

thank you for your attention guys,..actually, the pilot plant treated source water which is contained of high ammonia concentration,then nitrification biological process is choosen as pretreatment. I try to identify the NOM before and after nitrification. and the results showed HS,BuildingBlocks not removed ,Low Molecular Weight Acid and Neutral increased. I think because microbes can't degrade HS and BB, both are refractory organic matter.However, is it possible if LMW acid and neutral increased was caused by microbial degradation produced by-product such as propionate acid or something?i don't have experience about this kind of topic.please,share with me.thx

Thank you for your clarifications Hidayah. Humic substances and microbial decay products are recalcitrant to biodegradation as opposed to most LMW compounds including VFA's (acetate, propionate, ...) which can be degraded by a wide range of heterotrophs. Assuming that all these compounds are at (very) low concentrations in the source (well) water, then adsorption on activated carbon (with optional biological regeneration) will remove the residual organics.

Dear Hidayah! For what purpose will your treated water be used? Why do you need to remove NOM's as humic substances? If needed, color is most efficiently reduced by AOP, i.e. O3, UV, H2O2, Fenton, TiO2 alone or in combination ...

Dear Mr. Boris..the pilot plant will try to treat the source water contained of ammonia to be clean water. For my research, i want to know the fate of NOM in nitrification process. So, i try to identify the fraction of NOM such as BP.HS.BB,LMW acids and neutral. NOM will influence the efficiency in the downstream treatment trains...

NOM will indeed reduce the efficiency in downstream water treatment such as by fouling membranes especially NF/RO ones. Hence if NOM is present in the raw well water then this shall best be removed in the first step i.e. upstream of nitrification.

Hi Hidayah,

I agree with our colleagues on the degradation of organic matter by autotrophic bacteria and about the particulars of humic substances formed by molecules that are very large and very stable, whose degradation can be made by fungi and actinomycetes.

20 years ago, I tried removing humic acid from water supply, using fungi. I was able to remove 80% with HRT of 20 days.

ok, i got the point for humic substances, but how about LMW acid and neutral?why are those substances increse after nitrification/bological process?

That's a very good question Hidayah. Most likely, the answer can be found in the current biological treatment configuration and operation. Although this is unknown to the rest of us, I can imagine that the autotrophic nitrification (NH4 > NO3) step is followed by a heterotrophic denitrification (NO3 > N2) step requiring the addition of readily biodegradable organic carbon which may be overdosed (stoichiometrically) resp. underused (by the bacteria) resulting in the residual acid and neutral LMW.

Its water was sterilized? You have only nitrifying microorganisms in the system? If the water was not sterilized and if you do not have pure culture system, probably other microorganisms (other than nitrifying) partially degraded larger molecules, transforming them into smaller sub-products.

Dear Hidayah, according to my experience and knowledge, Bruno may well be right. To understand what is going on, you may also exercise writing down some kinetic equations and balance the left and right sides ...

Second, as I already said, NOM is well eliminated by AOP's. If you are economizing and have plenty of space in not too cold climate, try using bioremediation ponds or filters, e.g. as Sandra suggests. Nature may be so helpful! NB: But you will also have to help the Nature - be shure to properly balance the kinetic equations to know how to feed the bioremediation ponds / filters!

Dear Hidayah, a nice topic. I used HPSEC for characterisation of secondary effluent several years ago. When i put the secondary efflent into cooling room (4 degree) for several weeks (after 0.45 um prefiltration), I can find that the BP part decreased and the LMW and neutral part increased. I didn't do a mass balance, unfortunately. But I can imagine that some of the BP can be consumed by bacteria, this may lead to the formation of small molecules which can not be readily used by the bacteria in the water bottle. I can remember this phenomenon was reported in a biofilter treating surface water after certain operating time. It was supposed that some bacteria formed in the deep layer of the filter and lead to denitrification, and at the same time the release of some LMW organics. One thing may be important that the fractionation of water into BP, humics, BB and LMW... doesn't represent their specific nature, this is just a rough characterisation methods. It is difficult to consider which kind of organics increase. If you want to characterise the variation of NOM in nitrification process, maybe interesting to investigate with some other treatment procedure such as biofilter or UF or RO, to figure out how the increase of LWM organics influence the subsequent procedure.

Kind regards

Xing Zheng

thank you so much for all friends...xie-xie Mr.Xing Zheng, i also have the same opinion with your explanation and also agree with Mr.Boris,Mr.Bruno and Ms.Sandra