There is nothing like 'most suitable time' for withdrawing primary sludge.

Provision of continuous sludge pumping is desirable.Timer control pumping cycle may be necessary to achieve self cleaning velocity. Also ensure that each sludge hopper has an individual sludge withdrawal pipe at least 15 cm in dia.

The sludge pump to be used should be a self priming centrifugal.

Well,

Primary Treatment or Primary Sedimentation

•Settle solids for 2‑3 hours in a static, unmixed tank or basin.

•~75-90% of particles and 50-75% of organics settle out as “primary sludge”

•enteric microbe levels in primary sludge are ~10X higher than in raw sewage

•Little removal of enteric microbes: typically ~50%

Sincerely

Continuous sludge pumping is necessary I agree with Dr K N Sheth Sir

Sludge digestion is a biological process in which organic solids are decomposed into stable substances. Digestion reduces the total mass of solids, destroys pathogens, and makes it easier to wastewater or dry the sludge. Digested sludge is inoffensive, having the appearance and characteristics of a rich potting soil.

As mentioned by Mr. Hussien, primary sedimentation is settling of solids prior biological treatment of wastewaters. Thus, composition of primary sludge highly depends on the wastewaters. To understand primary sedimentation, I would suggest to go through some literature dealing with steps of wastewater treatment technologies to better understand primary sludge composition. I don´t know what your project or work is about, but primary sludge does not have constant composition and this needs to be taken into account when using it.

Dear Weam Mahdawi,

Sludge withdrawal should be exercised once in every 8 hours i.e. 3 times in one day and pump should be kept ON for such a period of time that it will pump out nearly 16.70 m3 of settled sludge in one batch. So you will be able to pump out 50 m3 per day in all the three batches. Generally SS concentration in settled sludge if goes below 10,000 mg/L, pumping should be stopped.

The sludge is generated in the wastewater treatment plant in the form of already present settle able solids, when settled in the PST, and in the form of biological cell mass, generated in the biological secondary treatment that settled in SST. The water content of the sludge is very high, and solids constitute very small part of it. Therefore before final disposal further treatment is required for this sludge to reduce water content and oxygen demand. Sludge is stabilized to (i) reduce pathogens, (ii) eliminate odors, (iii) inhibit, reduce, or eliminate the potential for decomposition, and (iv) improvedewatering characteristics of the sludge to reduce volume for disposal. There are four means to eliminate this nuisance condition through stabilization. They are (1) biological reduction of volatile solids, (2) chemical oxidation of volatile solids, (3) addition of chemicals to make conditions not suitable for bacterial growth, (4) application of heat to disinfect or sterile the sludge.

thank you for your answers

Thanks for the interesting question.

Here are a few thoughts to share re primary sedimentation.

1. Intermittent removal of solids is probably not a very effective and sound approach.

2. You may want to keep the SRT in the PST around 1-3 days, depending on the secondary biological process, and employ PST as a solids hydrolysis unit to enhance EBPR.

3. If the objective is to enhance biogas production, you may want to keep the SRT to a minimum.

4. You may also capture your primary solids downstream to an anaerobic selector in a short-SRT EBPR process, thereby enhancing the carbon capture and preservation for biogas production; We write more about this in the context of using such an EBPR combined with a photobioreactor:

Wágner, S.D., Radovici, M., Angelidaki, I., Smets, B.F., Plosz, B.G., (2016). Harvesting microalgae via an innovative bioflocculation approach and energy recovery from a bacterial-microalgal process. ALGAL RESEARCH, 20, 197-204. (full text uploaded on my ResearchGate account).

All the best, Benedek

Dear Dr. Weam Mahdawi,

Your question as stands would read as below: ( pl correct if otherwise, )

What is the most suitable time to withdraw- (n) the primary sludge from primary sedimentation tank to the digested process or next process .. ??

I totally abide by notings by Dr. Ramamohana Reddy Reddy Appannagari..

I do give due credits to -RRRA- for the excellent compilation of concepts in detail, well wishes and thanks for the same..

Process explained : 8 Nos. points :

1. Sludge digestion is a biological process in which organic solids are decomposed into stable substances.

2. Digestion reduces the total mass of solids, destroys pathogens, and makes it easier to wastewater or dry the sludge.

3. Digested sludge is inoffensive, having the appearance and characteristics of a rich potting soil

4. The sludge is generated in the wastewater treatment plant in the form of already present settle able solids, when settled in the PST, and in the form of biological cell mass, generated in the biological secondary treatment that settled in SST.

5. Water content of the sludge is very high, solids constitute very small part

6. Therefore before final disposal further treatment is required for this sludge to reduce Water content and increase Oxygen demand.-2 elements.

7. Sludge is stabilized for 4 Nos. factors- (i) reduce pathogens, (ii) eliminate odors, (iii) inhibit, reduce, or eliminate the potential for decomposition, and (iv) improved dewatering characteristics of the sludge to reduce volume for disposal.

8. There are four means to eliminate this nuisance condition through stabilization. They are (1) biological reduction of volatile solids, (2) chemical oxidation of volatile solids, (3) addition of chemicals to make conditions not suitable for bacterial growth, (4) application of heat to disinfect or sterile the sludge.

Even though, bit expensive can be done as cost-effective as possible.

General :

Pl. carry out sampling of the final product, in phases of time- say weekly..

At best it would take 3-4 weeks in tropical climate as Indian..

When you carry out final- sampling after the ... period, the output matter would appear resembling mud, and with no objectionable odour or texture, this matter is dried- (solar- duly aired) and can be used as nutrient soil,

If desired, more curing- maturing time can be afforded. weekly monitor..

Pl. arrange carry out the Tests as done for Soil for P-physical ,C- chemical , B- micro-biological elements,

If appropriate time has been afforded for remediation, it would be satisfactory and in order.

Inference on field:

After all, the complete accumulation of night-soil in OD areas, are all remedied by natural process and get transformed into soil etc..

well wishes, Prof. Ajit Seshadri, Vels University, Chennai. INDIA.

Primary sludge collected from the primary clarifiers is usually directed to the relevant primary sludge pump stations. From here, the destinations are ordered from most preferred to least preferred, with the normal destination being to the digesters. Perhaps, feeding the digester intermittently is the best advice (atleast 5% of the total volume each time).

thank you all for your valuable answers

Sludge, or residual solids, is the end product of wastewater treatment, whether biological or physical/chemical treatment. Primary sludge is from 3 to 6 percent solids. Treatment objectives are reduction of the sludge and volume, rendering it suitable for ultimate disposal. Secondary objectives are to utilize the generated gas if anaerobic digestion is selected as part of the sludge management strategy. In addition, an attempt should be made to sell/utilize the sludge as a soil conditioner rather than paying to dispose of it.

Sludge, or residual solids, is the end product of wastewater treatment, whether biological or physical/chemical treatment. Primary sludge is from 3 to 6 percent solids. Treatment objectives are reduction of the sludge and volume, rendering it suitable for ultimate disposal. Secondary objectives are to utilize the generated gas if anaerobic digestion is selected as part of the sludge management strategy. In addition, an attempt should be made to sell/utilize the sludge as a soil conditioner rather than paying to dispose of it.

The final destination of treated sewage sludge usually is the land. Watered sludge can be buried underground in a sanitary landfill. It also may be spread on agricultural land in order to make use of its value as a soil conditioner and fertilizer. Since sludge may contain toxic industrial chemicals, it is not spread on land where crops are grown for human consumption Where a suitable site for land disposal is not available, as in urban areas, sludge may be incinerated,completely evaporates the moisture and converts the organic solids into inert ash. The ash must be disposed of, but the reduced volume makes disposal more economical. Air pollution control is a very important consideration when sewage sludge is incinerated. Appropriate air-cleaning devices such as scrubbers and filters must be used.Dumping sludge in the ocean, once an economical disposal method for many coastal communities, is no longer considered a viable option.