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Peruvian Duckweed

Most of us, especially if you live on the Somerset Levels or the Norfolk Broads, often see our rhynes (ditches) and ponds covered in duckweed.

It is not the pest we think it is.

This week after nearly  two years preparatory work and 40 years of passion by Texas based  inventor of the system Paul Skilicorn. I am in Peru as part of Lyndon Water‘s management  team led by CEO  Ray Anderson working to deliver a truly unique water treatment project. Using duckweed as a key element in the treatment process we will  clean  urban  wastewater on an industrial scale and then turn it into potable drinking water to WHO standards. Water to the same standard that in Europe we take for granted 24 hours a day.

If all goes to plan in a little under 18 months people in an area of northern Peru will be free of a 30 year stench from its failed sewage treatment plant  and the region receiving additional potable water to increase availability of drinking water and reduce the strain on depleting aquifers.

October 2018 Update

Paul Skillicorn  recently left Lyndon Water and has set up a  competing business. with Ramiro Priale. 

Why Duckweed?

Duckweed is just about the fastest growing plant in the world. As duckweed grows it removes nutrients and  other contaminants converting suspended elements in wastewater  into usable biomass. We  separate and take the suspended solids for anaerobic digestion to generate power before the duckweed cleans the water. 

Duckweed under the Lyndon Water process is harvested and converted into fish food, animal feed, high protein superfoods or for energy generation. Some of the feed we produce will then be used to support Lyndon Water‘ s food  production at a new and nearby integral fish farm and Aquaponics facility that forms part of the Lyndon Water system. Nothing is wasted.

Glue 2’s  Duckweed Harvester and lagoon system.
Glue2’s vision of what future water treatment might look like this.

The harvester design  and the lagoon system design is by my  engineering consultancy  Glue2 Limited . We have also developed  a process for  concurrent transportation and processing of duckweed suitable for use in remote locations using minimal permanent infrastructure. All equipment and buildings are modularised and  based on ISO containers and dimensions.

We take wastewater and make drinking water, the waste we turn into food and power. What’s not to like?

When you  next see  duckweed covering a pond  or rhyne it’s not a pest but it’s cleaning up our water. It’s not all of the story of the process but it is the key.

Lyndon Water led by Ray Anderson off to see the Peruvian Government in Lima

Director Paul Bryant, CEO Ray Anderson, Lyndon Water in Country Manager Ramiro Priale & Chairman Lewis Jeffery

Letter of community support for our project just received 15th August 2017
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Retention of Concrete Consistency

Designing concrete mixes for specific purposes often raises questions that you don’t know the answers to. Familiar products have fallen into disuse and new products are just new. A recent project in Shetland required a mix able to get into areas of heavily congested reinforcement that had previously failed the first time around.

Highly plasticised mixes look and behave differently from “ normal “ concrete and  the current mix was  a 100% Portland cement mix that  appeared to have followed me over from Abu Dhabi with the same original contractor having developed a similar mix for two different projects. Shetland and Abu Dhabi having in common a lack of cement replacements particularly in the oil & gas industry. A situation further complicated  as  the current mix had a very high cement content was plasticised but not retarded making it very difficult to use in all but the simplest pours. It has  very little time to be placed.

The rework had a number of challenges that followed from the earlier pour.

  • Hanging shutters that obstructed the passage of concrete.
  • A relatively small volume; less than 10m3
  • Over detailing of reinforcement; surplus reinforcement that had not been removed during original  fixing.
  • Complicated shuttering and finishing that required considerable time to complete after the bulk of the concrete had been placed.

For the revised rework mix a new mix  with the following requirements was developed.

  1. A 10mm aggregate for  congestion and cover issues.
  2. Place using the chute from the back of the truck.
  3. Delay the setting time to around 3 hours.
  4. Retain the waterproof qualities of the existing mix.
  5. Characteristic strength of 35N
  6. Satisfy durability requirements for a Marine Environment.

TESTING & APPROVAL

Sika provided a S4 mix design based on the above requirement;  to obtain client approval and to understand what we had and how it worked a simple test was done twice.

Batches of the revised concrete  mix were mixed and held in a truck mixer replicating a long discharge time on site.

The truck mixer was progressively emptied over 3 hours.

Slump test were taken every 20 minutes and cubes at hourly intervals (1, 2 and 3 hours) for testing at 7 and 28 days.

Testing at EMN Plant’s Scatska Batching Plant in Shetland April 2017

RESULTS

they were very good

  • the mix stayed at or around the design slump only marginally dropping off in the last two results  but still within limits.
  • cube results were consistent and all passed.

LESSON LEARNT

One important thing that was noted was that the consistency (slump) potentially drops for a short period below the specification ,about 1 hour after batching was completed, and then regains the required consistency. It occurred on both batches.

The lesson for Contractors, Consultants  and QA /QC processes is that

  • The time from batching to the initial test is important and that there is the potential to reject concrete that is actually ok.
  • When doing trial mixes develop tests that explore  what could happen when a concrete pour goes wrong and placing of concrete is delayed identifying any characteristics that might explain a rogue test result during placing operations.