ENG421 (12c) – Desalination and Waste Handling - types of residuals Residual Treatment Management of Residual Liquid Streams Management of Membrane Concentrate Management of Residual Sludges

General Water Treatment Technologies (Week 4) Treatment technologies (unit operations and processes) used determined by what needs to be removed, inactivated or modified

Waste Handling (1 of 9) - aka residuals management planning, design and operation of facilities to reuse or dispose of water treatment residuals - wish to minimise amount of material that must ultimately be disposed of, by recovering recyclable materials reducing water content of residuals - cost of transporting and ultimately disposing of residuals major fraction of residual management costs → reduce quantity of material (economic solution) - must also minimise environmental impacts and meet regulatory discharge requirements - may impact on design and operation of water treatment plant

Waste Handling (2 of 9) Residuals from the treatment of water - sludges from water treatment processes - liquid wastes from water treatment processes - liquid wastes from processes to thicken process sludges to treat liquid wastes - gaseous wastes (e.g. offgases) from specialised water treatment processes

Waste Handling (3 of 9) Sources of solid residuals from the treatment of water

Waste Handling (4 of 9) Sources of liquid residuals from the treatment of water

Waste Handling (5 of 9) Sources of miscellaneous residuals from the treatment of residuals from water treatment

Waste Handling (6 of 9)

Waste Handling (7 of 9)

Waste Handling (8 of 9) Amounts of residuals generated up to 5 % of raw water entering treatment plant most becomes filter waste washwater (granular and membrane) contains <10% removed solids underflow from sedimentation basins contains only 0.1 – 0.3 % of plant flow but has most of solids removed

Waste Handling (9 of 9) Constituents in residuals (sludges and liquids) to consider : pathogenic micro-organisms Giardia cysts, Cryptosporidium oocysts turbidity, particles disinfection byproducts (DBPs) precursors in DBP formation (natural organic matter) total organic carbon (TOC) taste-causing compounds odour-causing compounds synthetic organic compounds (SOCs) manganese and iron arsenic and other toxic compounds radioactive material dissolved solids and salt normally return liquid from these wastes to treatment plant but may treat with separate facilities if concerns significant

Residual Treatment (1 of 6) Past treatment of residuals : discharge to nearby streams or rivers stored in lagoons spread on land (little or no processing) this approach led to : discolouration or increased turbidity of receiving waters build up of sludge deposits in receiving waters occupying large areas of land with constructed lagoons impacts on fish via increased water turbidity, pH, water hardness high salt levels in some situations sludge spread on land prevents or inhibits plant growth sludge mixed with soil has reduced impact (not too much)

Residual Treatment (2 of 6) Treatment of residuals : must understand properties of residuals (measure)

Residual Treatment (3 of 6) Treatment of residuals (cont) : Coagulation sludges produced by coagulation and natural settling of particles sludges collected in sedimentation basins and on filters

Residual Treatment (4 of 6) Treatment of residuals : Coagulation sludges (cont)

Residual Treatment (5 of 6) Treatment of residuals (cont) : Granular Media Filter and Membrane Filter Waste Washwater from the cleaning of granular or membrane filters

Residual Treatment (6 of 6) Treatment of residuals (cont) : Reverse Osmosis and Nanofiltration Concentrate liquid wastes high in dissolved solids and low in suspended solids concentrations of dissolved salts much higher than feed stream 5 – 10 times higher

Management of Residual Liquid Streams (1 of 2) treatment options flow equalisation with or without chemical addition reduces impact of intermittent high volume backwash flows lagoons with or without chemical addition batch sedimentation with or without chemical addition high-rate sedimentation with or without chemical addition dissolved air flotation granular filtration membrane filtration disinfection UV oxidation discharge to surface waters wastewater collection sewers

Management of Residual Liquid Streams (2 of 2) Management of residual liquid streams (cont) : High-rate clarification

Management of Membrane Concentrate (1 of 5) must consider volume of concentrate may be 50% of flow to plant environmental classification and regulations due to high salt levels treatment options membrane concentration may be followed by crystallisation or solar evapouration evapouration/distillation solar evapouration crystallisation deep-well injection discharge to surface waters wastewater collection sewers

Management of Membrane Concentrate (2 of 5) Management of membrane concentrate (cont) : evapouration/distillation boiling with submerged tube heating surface boiling with long tube vertical evapourator flash evapouration forced circulation with vapor compression solar evapouration rotating surface evapouration wiped surface evapouration vapor reheating process vertical tube falling film evapourator

Management of Membrane Concentrate (3 of 5) Management of membrane concentrate (cont) : solar evapouration evapouration ponds glass covered solar ponds consider effects of relative humidity wind velocity barometric pressure water temperature salt concentration rain

Management of Membrane Concentrate (4 of 5) Management of membrane concentrate (cont) : crystallisation convert thickened concentrate into crystals crystals dewatered in centrifuge or belt press dispose of crystals to landfill

Management of Membrane Concentrate (5 of 5) Management of membrane concentrate (cont) : deep-well injection pump concentrate into an injection well (1000s m deep) injection zone is usually brackish or saline aquifer under thick layers of impermeable rock prevents contamination of shallower freshwater aquifers

Management of Residual Sludges (1 of 8) treatment options

Management of Residual Sludges (2 of 8) Management of residual sludges (cont) : alum sludge 1. gravity thickening → chemical conditioning → centrifuge → landfill 2. sludge lagoons → decant recovery and recycle → landfill (or sewerage) membrane concentrate directly to : brackish surface water ocean deep-well injection sewerage

Management of Residual Sludges (3 of 8) Management of residual sludges (cont) : gravity thickening

Management of Residual Sludges (4 of 8) Management of residual sludges (cont) : dissolved air flotation thickening

Management of Residual Sludges (5 of 8) Management of residual sludges (cont) : sludge lagoons non-mechanical requires sufficient, cheap land (makes lagooning cost effective)

Management of Residual Sludges (6 of 8) Management of residual sludges (cont) : vacuum filtration

Management of Residual Sludges (7 of 8) Management of residual sludges (cont) : plate and frame filter presses

Management of Residual Sludges (8 of 8) Management of residual sludges (cont) : belt filters

References Masters, G.M., 1998, Introduction to Environmental Engineering and Science, Prentice Hall, Upper Saddle River, pages 286 – 287 MWH, 2005, Water Treatment Principles and Design, 2nd ed., John Wiley and Sons, New York (TD430 .W375 2005), pages 1429 – 1506, 1641 – 1708 Nemerow, N.L. et al, 2009, Environ Eng : Water, Wastewater, Soil and Ground, 6th ed., John Wiley and Sons, New York (TD430 .E58 2009), page 162 Parsons, S.A. and Jefferson, B., 2006, Introduction to Potable Water Treatment Systems, Blackwell, Oxford (TD430 .P37 2006), pages 165 – 176