From USEPA: "Stabilization of biosolids helps to minimize the potential for odor generation, destroys pathogens (disease causing organisms), and reduces the material’s vector attraction potential. One method of stabilization is to add alkaline materials to raise the pH level to make conditions unfavorable for the growth of organisms (such as pathogens). Where lime or another alkaline additive (for example, recycled kiln dust), is relatively inexpensive, alkaline stabilization is often the most cost-effective process for wastewater solids stabilization. This is particularly true where dependable markets for the alkaline product can be developed, such as in areas where alkaline materials are routinely applied to agricultural soils to maximize crop yields. "(www.epa.gov/biosolids/alkaline-stabilization-biosolids)

From my perspective, for municipal FSM systems using the technology, best to first concentrate the biosolids using sedimentation or some other process prior to dosing with lime. That will minimize the amount of high pH liquids, which could then be reintroduced into the liquids stream for treatment. One could also mix the effluent with water from hand wash facilities at the site, and even septic tank effluent from the facility restrooms to dilute the lime treated effluent while reinoculating the effluent with microbes. My guess is that traditional effluent treatment systems would function well in this type of scenario, although to my knowledge, that has not yet been tested. It would be very interesting to do some research on the effectiveness of ABRs or wetlands for dealing with lime impacted effluent to be sure.

Dear Kris and All

Query by kharallaxman is still unanswered. The issue has been discussed previously on the forum. Use of lime stabilisation at some sites in Philippines has been highlighted previously. You also mentioned it. However, it does not mention treatment technology of filtrate. Disposed of effluent on solid waste dumping ground is not a solution. pH may come to neutral as mentioned by kharallaxman. But what is time requirement?
Application of lime has been reported for some sites in Cambodia. If someone has report on treatment of effluent in that country, pl. share.
During previous discussion I had raised some fundamental query. Lime does not cause stabilisation. Lime stabilisation is a misnomer. Killing of bacteria / pathogens is not stabilisation. Purpose of septage management is the safe reuse of solid as well as liquid parts. Lime may have beneficial for one part but causes serious problem for another part.

Best
Pawan

kharallaxman wrote: Thanks for the response. The problem sought to be addressed here is not pH neutralization however - the pH after lime application is reported to come to neutral naturally. The question is how to make sure that biological treatment processes following lime application would not be compromised due to the dying of pathogens and halting of microbial degradation due to the lime application.

Not sure I can follow...

While the pH will probably decline a bit due to the drying bed process removing some precipitated lime and natural CO2 capture from the atmosphere, this will take quite some time and I doubt it will reach neutral levels easily. But again, theoretically speaking, as while I have visited such a lime treatment plant in the Philippines, I was not involved in the day to day operation and process optimization.

Thus the problem to my understanding is the high pH that will have a strong impact on any subsequent biological treatment process or natural streams if directly discharged (in the system I visited it was discharged into a solid-waste dump side and thus there was little to make worse). After all the two main purposes of adding quicklime are to stabilize/precipitate solids in the sludge and the same time rise the pH to levels that kills most of the pathogens.

However besides having to neutralize the pH, it might also be necessary to inoculate any biological treatment process with bacteria from a well running system as the percolate from the lime treatment system will have few beneficial bacterial left to colonize the biological treatment system by itself.

Thanks for the response. The problem sought to be addressed here is not pH neutralization however - the pH after lime application is reported to come to neutral naturally. The question is how to make sure that biological treatment processes following lime application would not be compromised due to the dying of pathogens and halting of microbial degradation due to the lime application.

pkjha wrote: It does not appear economically sustainable to add acid to lower pH from 12-13 to 7 for Kilo liters of waste water on daily basis. .

Yes, that is the conventional wisdom for waste-water treatment plants. It might apply to this specific situation or it might not...

I would guess if it is economically feasible to raise the pH to that level for all the wet sludge, lowering it again for just the percolate is probably feasible as well.

It does not appear economically sustainable to add acid to lower pH from 12-13 to 7 for Kilo liters of waste water on daily basis. .


Pawan

To my (theoretical) understanding it is the high pH (12-13) that kills the bacterial. Thus after de-watering the sludge in unplanted drying beds, the percolate can be pH adjusted to neutral levels (6-7) by dosing an acid to it.

I guess industrial grade sulphuric acid might be the cheapest and most easy to get option, but citric, lactic or hydrochloric acid will probably work as well with less environmental impact. Lactic and citric acid might even be beneficial to the subsequent biological treatment process as both should also work as a carbon food source for many bacteria.

Worth a try for sure

P.S.: Please ensure that your stock of lime and acid is well separated and that your workers are acutely aware of the danger of mixing highly concentrated acids with quicklime directly!

Dear dmrobbins and colleagues,
Greetings !
This is to seek if any evidence has emerged on - how long after lime application regrowth of pathogens may occur again for normal biological process to take place in the units such as Anaerobic Filter and Horizontal Flow Wetland receiving liquid separated in un planted drying sand beds from sludge treated with lime . Or is there any dose or extent of lime application that can without inactivating all the microbial activity just make the sludge dewater-able in the drying bed without affecting the downward biological process in anaerobic filter and horizontal flow wetland significantly? Or alternative, how this could be addressed?
This is in connection with an emergency FS treatment plant where the faecal sludge is quite fresh (about three months old) and there is lack of space to store the FS for a longer time before application in the unplanted drying bed. With lime application it is supposed that the FS will become dewater-able quickly in the unplanted drying bed.
Thanks.
Laxman

Hi Pawan,

It is a great suggestion and I think it would be easy to test. Recommend setting up a simple jar testing bench scale treatability study. Easy and inexpensive, and will provide you with information on the required dosing of hydrated lime for this application. If you try it, please let me know what you find out.

thanks for the post,

Dave

Dear David

Thanks for the reply.
I am providing consultancy for septage management for 6 cities in Rajasthan State in India, supported by ADB. I am providing unplanted or planted sand filter beds (depending on site condition) followed by treatment options for effluent. I am not recommending lime due to its recurring expenses and precautionary measures required during handling by semi-skilled workers at the sites. Moreover, in the State, atmospheric temperature goes up to 500 C, sufficient to kill pathogens on drying beds. If frequency of loading is decreased by increasing number of beds and maintaining the sludge height of 20 cm, dried solid mass of desired level can be obtained with least chance of survival of pathogens.
Effluent from filter beds has high BOD – around 500 mg/l. It’s challenging to treat it to the acceptable level of discharge or reuse. Lagoon is not suitable to meet the discharge norms. Moreover, it requires large space- not normally available in urban areas. Anaerobic system is also not suitable to meet the discharge norms. I will use aerobic system with bacterial growth media. Lime is also not suitable as in such case population density of bacteria in effluent will definitely reduce, resulting in lower efficiency of the treatment system.
One simple suggestion-- Is it possible to use lime with higher doze in the septage only during the last loading of the filter bed? In such case lime will kill pathogens in solids on filter bed. Earlier effluent will have normal population density of bacteria. Effluent of last day will have little volume, of course with higher level of lime concentration. But total concentration will be much lower with little or no change in pH.
Regards
Pawan

Dear Pawan,

Thanks for your questions. First it is important to know that lime stabilization will not eliminate all of the pathogens, but certainly most of them. Also, it is more accurate to say that the process limits regrowth of bacteria, and not that there will be no regrowth. We don't want to over-sell the technology.

It is a good question about the ABR function. From our experience, the use of the ABR after the lime stabilization process functions more as a mechanism for additional physical separation for whatever solids remain in the wastewater stream after the sand filtration, where the bulk of the suspended solids are removed. The ABR also provides detention time of between 1 and 3 days which allows the pH to drop to a level more suitable for subsequent treatment, such as the constructed wetlands.

As for the term "stabilization", it has actually been used for years. The US Environmental Protection Agency utilized it back in 1978 in their "Full Scale Demonstration of Lime Stabilization" document that looked at different application rates of hydrated lime for wastewater, return activated sludge, and septage. I would suspect that there actually is some degradation of the biosolids that occurs from the reaction of hydrated lime and sludge.

Thanks again for your comments. Please advise if you are planning any trials. I just returned from Myanmar where Oxfam has demonstrated a full scale system serving more than 50,000 people. We are also trying it on a much smaller scale using the in-pit lime stabilization process first trialed by iDE in Cambodia. Seems to have really good potential there.

Dave

Dear David and All
I failed to see your earlier post on lime stabilization for septage management. The topic is much relevant for many countries. There are several papers/ guidelines in different countries, highlighting use of lime stabilization for sepatge management. I have a few queries:
i. Application of lime to increase pH to12 will definitely eliminate pathogens, other bacteria and helminths from septage. The Implementer's Guide of USAID also mentions that there is no chance of re-growth of bacteria when treated with Lime. It also mentions that after passing septage through sand filter bed, effluent should be treated through ABR technology.
ii. Now the simple query arises how a biological treatment system like ABR would function for the treatment of effluent having such high pH and without presence of bacteria in the system ( bacteria are already eliminated by using Lime).
iii. The Guide uses terminology— Lime stabilization. I think function of lime is only to eliminate bacterial and other pathogens. It never results in stabilization of organic matters. Stabilization is a completely different term from pathogen free environment.
I’ll be happy to have response from you and other members of the Forum.

Regards
Pawan