The Process

constructed wetlands group reed bed technology sludge removal biosolids

Our process treats wastewater utilizing anaerobic digestion, and the resulting sludge material is transferred to Phragmites australis reed beds, where the sludge is dewatered and excess nutrients are removed.

Characteristics of Phragmites

  • Rhizomes and emergent stalks has system of nodes
  • When nodes are engulfed by biosolids, they form adventitious secondary root system
  • Secondary lateral root system increases microbial habitat and aids in dewatering
  • Can exist in six feet of water for long periods of time and survive in desert conditions
  • Propagates almost exclusively by vegetative means
  • Percentage of seed that is viable needs stringent condition to grow: seed is light obligate and can grow only in specific and steady depth of water

Requirements of Reeds

  • Well stabilized sludge with 21-30 days retention for aerobic sludge and 45-60 days retention for anaerobic sludge ideal for volatile solids reduction
  • Proper aggregate for maintaining dynamic and consistent flow
  • Knowledge of sludge quality-metal concentration, oil/grease content, pH, use of polymers, floculants such as alum
  • Knowledge of climatic conditions
  • Adequate sizing of beds for optimal loading cycles

Planting

  • Plant stock is two week prepared grade A rhizome (roots)
  • Planting season is from April to November
  • Beds are carefully prepared for planting
  • Determining size of bed depends upon climatic conditions, influent characteristics, type of treatments and biosolids processing, wastewater flows, and infiltration and peak flows.

Construction of Reed Bed Varies

  • Concrete side walls, freeboard, or earthen berms
  • In all cases, PVC liner is used to make beds impermeable
  • Perforated under drain system and specific gradations of sand and gravel; samples and gradation reports approved by CWG.
  • Protocols are tailored and provided by CWG to each facility in the form of an operations and maintenance manual.

Harvesting of Reeds at the Seasons End

  • Significantly decreases biomass in beds
  • Partial removal of metals helps to lower metal levels in accumulated biosolids over time
  • Reeds have greatest affinity for zinc and copper
  • Nine to twelve inches of stalk is left to aid air transfer to rhizome and promotes drainage in winter
  • Harvested material is disposed of through burning, composting, landfilling, baling or chipping
  • Evacuating a residual from reed beds follows established protocols by Constructed Wetlands Group.
  • Disposal of residue can be used for
  • covering solid waste at landfills,
  • stabilize mine reclamation areas, or
  • agricultural application.
  • Biosolids residue has been screened and composted for removal
  • of vegetative matter

Cost Savings are Achieved Through

  • Low maintenance
  • No offsite removal of sludge for six to ten years
  • 90% reduction in volume of sludge removed
  • Increased overall efficiency of wastewater facility