Category: Treatment Technologies

Hydrocyclone Demonstration Test

3/30/2015

A small-scale hydrocyclone was set up in a test rig and a trial was performed to determine its potential for removing fine solids from vegetable washwater. The term ‘hydrocyclone’ refers to a cone-like structure where waste is separated out of wastewater. They can be run singularly or in a parallel system; the piece of equipment tested employed several small hydrocyclones running in parallel within a larger unit.

The unit was installed on top of a barrel with an inlet, outlet, and waste outlet so that the water could cycle through the system (Figure 1). A solution of muck and water was prepared; 1 L of muck was sieved through a 200 micron screen to remove roots and coarse solids and added to 150 L of water.

Figure 1: Small scale hydrocyclone test rig

Figure 2: The path of wastewater, treated water, and waste (A) through the unit and (B) through a single hydrocyclone [Source: A: HMGA Water Project; B: TangShan Dachuan Machinery Co., Ltd., 2013]

In this system the water is cleaned using 16 hydrocyclones running in parallel (Figure 2). The coarse solids are collected in the lower hopper and are removed through the outlet. Within the hydrocyclone, the wastewater is pumped in through a tangential opening at the top (Figure 3) which causes the water to rotate (CSI, 2009; TangShan Dachuan Machinery Co., Ltd., 2013). The swirling water creates a centrifugal force which where the heavy objects move to the outside and the lighter objects move to the centre (Figure 2B) (CSI, 2009). The solids pushed to the outside will continue to spiral downwards and exit to a waste collection tank (Figure 4). The lighter solids and liquid spin upwards and exits through a short pipe; this pipe extends below the inlet to ensure the entering wastewater doesn’t exit immediately (TangShan Dachuan Machinery Co., Ltd., 2013).

Figure 3: Openings to the top of 16 hydrocyclones

Figure 4: Collected waste

The pressure at which the wastewater is pumped through the system is important (TangShan Dachuan Machinery Co., Ltd., 2013). If the pressure is too high, there isn’t enough time to for the waste to separate from the liquid and fall out. If the pressure is too low, the speed of the swirling water is insufficient to separate the waste.

The results of this test will be shared in upcoming article.

References

CSI. (2009). FAQ. In Hydrocyclone. Retrieved March 26, 2015, from http://www.hydrocyclone.com/faq.htm
TangShan Dachuan Machinery Co., Ltd. (2013). Working Principle of Hydrocyclones. Retrieved March 6, 2015, from http://shaleshakerdc.com/working-principle-of-hydrocyclones/

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Filter Bags Demonstration Site

1/26/2015

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One technology under examination by the project is filter bags. They are made out of fabric and are available with different sized pores. Wastewater is pumped into the bag and the sediment is caught by the fabric while treated water is strained out. The water is then collected and continues through further treatment if necessary.

Figure 1: A filter bag on the collection table above a tank with a pipe to return treated water to a settling pond (left) and an expanding bag (right)

In order to test the system, a pump was placed at the inlet of a settling pond to send a sample of carrot washwater to a scaled-down filter bag (Figure 1). The washwater was pumped in and clearer water flowed out of the bag. The bag was successful in straining out both pieces of carrots and soil particles (Figure 2).

Figure 2: Inflow of vegetable washwater at the top and outflow from the filter bag at the bottom (left) and solids filtered by the bag (right)

There were two issues with the system identified by this test. First, the pump sending the water to the bag was plugged several times by large chunks of carrots. Those larger pieces would either have to be removed earlier or chopped prior to the filter bag. Second, the bag clogged due to the colloids in the water and ruptured at the seam when the water had nowhere to exit and pressure built within the bag. The addition of coagulants would reduce this problem by clumping the colloids prior to the bag.

The filter bag system was certainly successful at removing solids from the washwater and since they are collected in a bag, the discarding of the waste is straightforward. Unlike settling ponds, which have to be dug out on a regular basis, the bag can simply be replaced with a new one when full.

A larger sized filter bag will be tested in the future to further review the benefits and challenges this system presents.

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The Trouble with Muck: Size

11/3/2014

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A common test, called the Mason jar soil test, is suggested for home gardeners to decipher their soil type. The basic concept is to put water and a scoop of the soil into the jar, shake to thoroughly mix the soil and water, and let it stand. The sand will settle to the bottom first, followed by the silt, and finally the clay will fall out of suspension. The sand will settle in a minute, the silt will take a few hours, and clay will stay in suspension for a full day. The soil type is then determined by measuring the depth of these layers. But there’s more to soil than sand, silt, and clay. The fine organic matter particles are the last to sink and the large particles will just stay afloat.

Diagram (left) and example (right) of a Mason jar soil test
[Picture sources: (l) Pinkney (2010) and (r) Three Easy Soil Tests (2010)]

The vast majority of soil types involve varying amounts of sand, silt, and clay with a minimal amount of organic matter. Muck soils are unique in that they have anywhere between 20 and 80% organic matter.

Settling ponds or tanks, a scaled-up version of a Mason jar, is a method used to remove suspended solids from different types of wastewater. The wastewater is pumped into a large holding tank where it is held. The heavy particles will fall out of suspension and sink to the bottom leaving clear water to exit the pond. But, as the Mason jar test shows the time that wastewater needs to stay in the pond depends on the soil type.

So, settling ponds, whose entire purpose is to give particles time to sink, and muck, a soil type resistant to sinking, are a mismatched pair. They can still work together if the additional time for the muck to settle out is taken into account or as one part of a multi-step treatment process.

References

Pinkney, D. (2010, August 1). Starting a Garden - Understanding Your Garden Soil. In Gardening Info Zone. Retrieved October 15, 2014, from http://www.gardeninginfozone.com/starting-a-garden-understanding-your-garden-soil
Three Easy Soil Tests. (2010, May 21). In Cultivators Corner. Retrieved October 15, 2014, from http://cultivatorscorner.com/what-is-soil-made-of

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Hydrocyclone Demonstration Test

Filter Bags Demonstration Site

The Trouble with Muck: Size

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