Ecological Engineering in the Tropics

Costa Rica – MSU / UCR – December 27, 2014 – January 10, 2015

Liquid/Solid Separation – John

Liquid-Solid Separation

(water filter described in Food and Agriculture Organization:

water filter described in FAO

There are a few sites that we will visit that will utilize methods for liquid-solid separation. The first will be the hydroelectric plant in Tilaran. Here is a diagram from another hydroelectric power plant

Red circle is where sediments are collected

Red circle is where sediments are collected

If the hydroelectric plant takes in too many sediments, it will damage the turbines, which are expensive to replace and maintain.

(picture from Andritz Hydro)



The coffee processing operation we will visit in Alajuela will definitely use liquid-solid separation techniques, even if they are just brewing a cup of coffee!

But they need to do much more than that as well. The fruit of the coffee berry must be removed to expose the seed, which is the “bean” we roast, grind, and brew to make our morning beverage. The fruit of the coffee berry is removed in different ways in different facilities. Some processing plants use vast amounts of water to remove the pulp.

Here is a video of some farmers using the “Wet method” to process their beans. It will be interesting to see how the coffee farmers we visit use water for their processing, and how they separate the pulp from the water after the process!


Our team project on the 8th and 9th of January at the Fabio Baubrit Moreno station all revolves around liquid solid separation. We need to design a method of separating the solid products and the liquid effluent from the anaerobic digester at the agricultural station before it goes into the wetland for purification. Here are some designs for filters we looked at as a group before departing!

swirl filter

swirl filter II


I look forward to seeing all different places that have to be mindful about separating their solids and liquids!





Happy New Year!

This has been an incredible few days. It has been inspiring and a necessary addition to my education!

I have a bit more to report now on the topic of liquid/solid separation.

You can find in the day-blogs that our group visited two out of three power plants in a series of 3 hydroelectric power generating plants. The folks at ICE (Costa Rica’s public energy company) showed us their beautiful turbines, tubes, and tanks, and they shared some great details of their operation.

Here is Ronald with a diagram of the series of power plants



The picture shows ICE’s three dams and associated canals. The large body of water between mountains is a man-made reservoir that feeds the system. Two towns were submerged in the creation of Costa Rica’s largest lake. Here is some more information, The lake is 30 km long and 5 km wide at its widest point. A large mass of long grasses were submerged as well with the flooding of the lake. The inlet to the tubes that deliver water to the turbine began to clog and also the expensive turbine blades were damaged with the solid content in the working fluid. It was mandatory to remove and prevent these solids from entering the system.

At first, a German team of divers and mechanics were hired to clean the filters for a manual removal of the decomposing grasses. Eventually the Costa Ricans were trained and have been able to monitor the dams and inlet filters. This manual technique is not advanced, though they have installed a mechanical scraper to push away debris that might be caught on the filter.

Here is an intense feature of the water system and sediment removal. Sediments wash through the system and eventually collect in the series of reservoirs. About every two years, they flush all liquid out of the reservoirs through immense radial gates and send in machines to dredge the sediments from the beds. There are three main sources of sediments rushing into the water system for the dams: sediments in runoff on dusty rural roads, landslides, and the erosion on riverbanks.

The reservoirs were originally dredged every five years, but now they have to be maintenanced every two years. Here is a website documenting increased erosion in Costa Rica (

These important factors showcase the need for an integrated approach to liquid/solid separation. As we approach our project for the anaerobic digester, hopefully we can analyse many factors that contribute to the amount of solids in the effluent. We can look not only at separating the solids after the effluent is ejected, but maybe also at the reason for all the solids present in the effluent.

Pura Vida! More to come soon!




January 15, 2015


I’m home now, sitting in one of the computer labs of MSU’s Agricultural Engineering building. It is about -9 degrees Celcius here, a stark contrast to our nice weather in Costa Rica. I think most of us wish we were back at the beach!

I want to give a short report on the liquid/solid separation in each of the banana, pineapple, and coffee operations that we visited throughout the week. For a look in more detail at each trip, take a look at Nate’s (banana), Charlotte’s (pineapple), and Jackie’s (coffee) blog postings.

First, the bananas!

You can see how much water is involved with the process!

You can see how much water is involved with the process!

When researching wastewater treatment of refuse from banana processing operations, I came across a project from EARTH University, one of the places we visited earlier in our trip. Their research investigated the direct use of banana processing wastewater as fertilizer vs introducing effective microorganisms to make a value-added fertilizing compound.

The separation process that we saw in the banana processing only involved a few mechanical filters before the water was released into drainage channels.

Series of filters to trap large solids.

Series of filters to trap large solids.

The hands and fingers of the banana bunches are cut down into smaller amounts. All these cuts are places for sugars to seep into the water, making that liquid rich in organic compounds.

If these organic ingredients are flushed too soon into larger water supplies, environmental damage is probable.

Seeking options for banana wastewater liquid/solid separation, Mohamed Nageeb Rashed has investigated using different adsorption techniques for their removal. He proposes adding various compounds to the wastewater to attract undesirable components in the water for easier removal. There could have been more with the liquid/solid separation at the banana plant!

The water used in the pineapple plant was also primarily used for washing and insecticidal/fugicidal treatment.

Conveyor belt separates the pineapples from the wash-water

Conveyor belt separates the pineapples from the wash-water

The pineapple plant we visited also recycled their water as much as possible to reduce water consumption.

The pineapple processing operation was conscious of the solid waste, and it was either used for animal feed or crop fertilization. Its liquid waste was not referred to as an asset though. This article explores the possibility of using the waste from pineapple processing lines to produce “Nata de pina” a creamy desert substance that can go with fruits.



The last processing line conscious of liquid/solid separation was  coffee. They had many technique for separating liquids and solids, including evaporation through sun-drying!

Beans drying their musilage in the sun

Beans drying their musilage in the sun

We visited what is called a wet-process plant. That means very much water is used in the process. They were building an ethanol producing operation for the wastewater. Coffee wastewater is full of pectin compounds that can be used in bioenergy production. A member of our group, Juan Pablo Rojas Sossa also was assisting Coopedota in their efforts to install an anaerobic digestion system for their wastewater.

In these plants, they needed liquid/solid separation most for separating their product from washwater, or water that was being used to transport the product, like the coffee beans and bananas. The wastewater still needs more implements installed in each place to separate solid pollutants, or to extract substances that could be valuable for other production.


One thought on “Liquid/Solid Separation – John

  1. Hi John! I really liked how you talked about the different kinds of seperation processes.

    I think that swirl filters were a great option for the design project because they can be built to any size and require minimal materials/maintenance.

    On a larger scale: During our coffee plant tour, the manager talked about how these days the river is flooded with city waste. I think that your first diagram is a good way to filter large amounts of water and I think this could be integrated to help clean river water. But like the manual cleaning of hydrodams (as mentioned above) I am not sure how much maintenance is involved with such large scale water treatment fascilities.

    I look forward to seeing how our design works out and all our areas for improvement!


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