Author: Rose Lenihan, chief executive officer, Dionergy Ltd The management options for the collection, treatment and disposal of sludge were addressed in the EPA Strive Report Series No 123 prepared for the EPA by Ryan Hanley Consulting Engineers and published in 2014. Storage, transportation and disposal of waste sludge were identified as immediate challenges to municipal authorities. The immediate cost of transportation of waste sludge to central hubs is one challenge but the greater challenge is the infrastructural cost of increasing the availability of storage at hub sites as they are currently at capacity. In agriculture production and processing, access to adequate land banks is already a challenge in the management of expansion and growth and represents a significant existing transportation cost to the sector. Dionergy’s aim is to cost-effectively treat waste sludge, using aerobic digestion, to reduce transportation and storage costs and maximise the use of land banks available for spreading municipal waste and agricultural slurry.

Trial overview

This article present the results from a recent trial of Dionergy’s EL300 unit conducted in a commercial piggery in Ireland. The purpose of the trial was to benchmark the performance of the Dionergy EL300 aerator in pig slurry with reference to solids and nutrient content over time. A technical report was completed by an independent consultant at the end of the trial. The trial parameters and results are set out below. All sampling and analysis were carried out by an accredited lab for the duration of the trial.
Parameter 19-Jun-15 21-Aug-15 % Reduction
Total Solids (kg) 11941.02 4594.59 61.52%
Volatile Solids (kg) 8592.48 2923.83 65.97%
Ammonia (kg) 953.16 605.9 36.43%
Kjeldahl Nitrogen (kg) 1221.48 712.53 41.67%
Total Phosphorous (kg) 126.36 31.941 74.72%
Hydrogen Sulphide (ppm) 61.61 0.0044 99.99%

Trial details

Some 250 m3 of pig slurry was introduced to an open tank on the first day of the trial. The tank was filled to a depth of 1.9m.  Then 50m3 of additional slurry was added during the trial period, other than that, the tank did not process throughput and the final depth at the end of the trial was 2.2m. The Dionergy unit is powered by a 0.75Kw motor, the unit sat on the surface of the slurry on a float in the middle of the tank secured with wire ropes. The trial assessed the impact of the Dionergy EL300 unit on solids content, breakdown and stability over time, nitrogen content and its constituent parts as well as phosphorous content and its readily reactive component as well as hydrogen sulphide in and around the tank.

Trial results

There were 27 samples taken from 150mm below the surface level of the slurry. An additional five samples were taken in the final week of the trial at a depth of 1960mm below the surface, 240mm from the floor of the tank. The samples were taken to determine if there were significant changes in the solids and phosphorous readings at that depth. The variances from those samples were within 10 per cent of the samples taken from below the surface. There was a 74 per cent difference in the phosphorous readings taken from the slurry at the end of the trial compared with the readings at the start of the trial. The total and volatile solids were reduced by more than 60 per cent and the TKN and ammonia by 41 per cent and 36 per cent respectively. The tank contents were spread via an umbilical, pumping the slurry directly to the field for spreading. There was 300mm of residual solids at the bottom of the tank once the liquid slurry was removed. Three samples were taken from the residual sludge on the floor of the tank and analysed for total phosphorous. The phosphorous readings taken were considerably higher in the remaining quantity of sludge, which provides potential opportunities for the removal and treatment for phosphorous recovery, depending on volume.

Trial implications

  • Cost-effective solids digestion potentially reduces the cost of transporting solids significantly;
  • A potential to increase the slurry: land bank ratio for spreading due to the phosphorous readings;
  • Significant odour reduction both in the tank and when spread;
  • Treated slurry is already broken down, and is readily bio-available decreasing the risk of run-off.
[caption id="attachment_26033" align="alignright" width="300"]aabets2 The spreading of untreated slurry[/caption] [caption id="attachment_26034" align="alignright" width="300"]aabets3 Spreading of treated slurry[/caption] In summary, there are both positive economic and environmental implications from the trial. The full report of the trial is available on the Dionergy website. There are also videos on the site which illustrate effectively the digestion that has occurred in the slurry during treatment.

Applications

Dionergy’s treatment solutions are plug and go installations that sit on floats on top of the waste in tanks. They are secured using wire cables. EL300 units weigh less than 30kgs and installation and removal takes less than half a day. Units require access to air and are most suitable for open air tanks. To date, they have been installed in small municipal waste sludge tanks, large holding tanks and in open slurry tanks on farms. Dionergy will continue to build on existing data sets for the treatment of waste sludge in the municipal and agri-sectors and results will be published on our website as they are released. Please feel free to contact Dionergy via telephone or email with questions about the trial and the units. Michael Harnett is Dionergy’s business development director and is available on 085 704 5440 and via email: mharnett@dionergy.com