Hi everyone I have a municipal wastewater treatment plant with aerated lagoon process with capacity 1500 cm/d and with: pretreatment part (screening and aerated grit removal tank) aerated lagoon ( 2900 m2) with 4 aerators with unit capacity 25 kg/hfacultative lagoon (2800 m2) with 2 aerators with unit capacity 25 kg/hClarifier (490 m2) This plant built since 1991 receive now 2500 m3/d. The main problem is the bad quality of treated water (SS > 120 mg/l and whitish look) and the sludge fails to settle How to do ?

Mr. Chaabouni, You have measured a high effluent suspended solids of 120mg/L, but have you also measured the effluent BOD5 or COD? Often TSS and BOD are related, but not always, and the TSS to BOD ratio provide more information. I have a few ideas about your system and what may be happening. If you would like to discuss further, please contact me at ARice@aqua-aerobic.com It is very possible your plant is overloaded, and requires more aeration in order to meet treatment, since you have expanded the flow rate 1500m3/day to 2500m3/day. If you have influent loading criteria (eg: BOD, TKN, etc), you can estimate if you have enough oxygen from your existing aerators. I am separating this into three different topics: poor effluent quality, poor settling in your clarifier, and a white color. Regarding the Poor Settling 1. My first thought is that you do not have enough aeration in your basin for biological treatment. It is well understood that having a low dissolved oxygen level will lead to a biomass that is not able to flocculate effectively in lagoon systems ("High Performance Aerated Lagoon Systems" by Linvil Rich, pp. 204). The solution to this is to add additional aeration equipment. 2. My second thought is perhaps you are short circuiting your basin. Although your theoretical detention time is 2.3 days, some of the water may be short circuiting and reaching your effluent in less time. A young sludge below 2 days does not flocculate well and would lead to high suspended solids. The solution to this would also be to add additional aeration equipment. 3. You may be releasing dissolved gasses or denitrifying in your clarifier, which will float solids to the top similar to a dissolved air floatation system. This too may be an issue with aeration. All three of these issues could occur directly from your increase in flow rate. There's other possible issues (eg: the placement of your aerators is shearing flocc by the effluent), but you would expect something like to have always happened rather than only happening recently. Regarding the poor effluent quality 1. The high effluent suspended solids is clearly related to poor settling in your clarifier and facultative lagoon. 2. You may also be getting poor biological treatment in your lagoons, depending on your influent loading criteria. To achieve good treatment in an aerated lagoon, you usually want 5+ days of detention time. You have less than half of that. In order to get good treatment, you almost certainly need more aeration and mixing power to (1) transfer additional oxygen and (2) improve mixing, which will improve the kinetic removal rate of the biomass in your lagoon. Regarding the white color - In my experience, I have only seen three things that have caused a white effluent: i. You may have insufficient aeration that is leading to anaerobic decay on the bottom of your basin, and dissolved or undissolved gasses may be coloring the wastewater. ii. Calcium carbonate or calcium phosphate could be precipitating out of solution. You can measure your water pH, alkalinity, and Ca content in order to shed light on this. iii. Certain industrial wastewaters - especially sugar beets. This is UNLIKELY in your case because it is a municipal system. I have also heard stories of cilates creating a milk-like effluent, but I have not seen that personally. At any rate, please don't hesitate to email me at ARice@aqua-aerobic.com if you would like to discuss your application further. My expertise is in the design of aerated lagoon and facultative lagoon systems, and wastewater aeration systems, and I can help you predict how much additional aeration equipment you will need, and what the most effective aeration equipment will be for your basin.

Aerated Lagoon

Published on December 5, 2019 23:45 by Maymoun CHAABOUNI in Technology

Hi everyone

I have a municipal wastewater treatment plant with aerated lagoon process with capacity 1500 cm/d and with:

pretreatment part (screening and aerated grit removal tank)
aerated lagoon ( 2900 m2) with 4 aerators with unit capacity 25 kg/h
facultative lagoon (2800 m2) with 2 aerators with unit capacity 25 kg/h
Clarifier (490 m2)

This plant built since 1991 receive now 2500 m3/d.

The main problem is the bad quality of treated water (SS > 120 mg/l and whitish look) and the sludge fails to settle

How to do ?

Taxonomy

Aeration
Waste Water Treatments
Wastewater Treatment
Wastewater Treatment Plant Design
water, wastewater, reclaimed water, water resources planning
Lagoon