Using the "resting pool" method to solve the problem of scum crust in digesters

August 06, 2025

In rural areas, many households use hydraulic biogas digesters to convert organic waste into energy. However, over time, some of the raw materials—especially floating ones like plant residues—rise to the surface due to buoyancy. This leads to the formation of scum and eventually hard crusts on top of the digester. Crusting has become a major issue in these systems, significantly affecting their performance. Long-term studies have shown that digesters primarily fed with human and animal waste tend to develop crusts 18–25 cm thick after one year, while those using weed or straw as main feedstock can see crusts grow up to 25–35 cm thick. These crusts block gas accumulation, reduce the effective volume of the digester, and lower the efficiency of raw material utilization. As a result, gas production decreases, and severe crusting can even turn a functional digester into a "diseased" or "waste" pool. To address this problem, many biogas technicians worldwide have developed agitation and crust-breaking devices. Some of these tools are quite effective, but they often add complexity, increase construction costs, and make widespread adoption difficult. In response, we have implemented a method called "pool resting." This involves stopping the digester for 5–7 days annually. After more than five years of testing, this approach has proven highly effective in managing sludge and crusts. The process involves several key steps: First, all the biogas in the digester must be used up, and all distribution system valves should be opened to ensure the digester is at zero pressure. Next, disconnect the gas outlet hose so that any remaining gas from daily production can escape naturally. Then, continuously add water to the digester until it is fully filled. Once the system is sealed and stopped, it will rest for 5–7 days. During this time, the floating sludge is soaked in the slurry, and under constant pressure, it settles down as sediment. The accumulated sludge can then be removed using an automatic slagging device. It’s important to note that the "pool resting" method should be carried out during periods of low gas production, typically in winter. Also, during the resting period, open flames must not be used near the gas outlet, and no fire tests should be conducted on the pipeline to avoid explosions. At the same time, a full inspection of the digester's cover plates and the gas distribution system should be done to identify and fix any issues promptly, ensuring safe operation. This method not only helps maintain the efficiency of the biogas system but also extends its lifespan, making it a practical and cost-effective solution for rural households.

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Specification:

Product Model:

JX40

Accuracy:

±1.5mm (0.06 inch)

Measuring Unit:

metre/inch/feet

Measuring Range:

0.03~40m (0.01 to 131 ft)

Measuring Time:

0.1~4 seconds

Laser Class:

Class II

Laser Type:

635nm, <1mW

Waterproof & Dustproof :

IP54

Auto Laser Off:

60 seconds

Automatic Power-off:

480 seconds(8 minutes)

Lighting:

white LED

Datum Option:

Can choose Front edge or end piece edge as datum

Battery Status:

Y

Signal Strength Display:

Y

LCD display:

2 inch large screen

Display illumination and multi-line display:

Max 2 displays

Data Memory:

Y (allow 20 values)

Backlight display:

Y

Continuous Measurement:

Y

Min/max Measurement:

Y

Addition/Subtraction(Distance/Area/Volume):

Y

Area/Volume/Pythagoras Measurement:

Y

Battery Type:

AAA alkaline battery(2*1.5v )

Weight:

about 80g

Dimensions(L*W*H):

4*2*11.5cm

Auto correction and error report technology:

Y

Operating Temperature:

0-40 ℃(32-104 ℉ )

Storage Temperature:

-20~60 ℃ (-4~140 ℉)

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