Chapter 5: Other Advanced Wastewater Treatment Processes

Transcription

1 ENGI 9605 Advanced Wastewater Treatment Chapter 5: Other Advanced Wastewater Treatment Processes Winter 2011 Faculty of Engineering & Applied Science 1

2 5.1 Suspended solids removal 1. Suspended solids left in wastewater after conventional treatments (Viessman et al., Water Supply and Pollution Control, 2009 ) 2

3 Removal of suspended solids from the effluent of a conventional treatment plant necessary to reduce the organic content or to pretreat the wastewater from subsequent processing Effective disinfection requires removal of suspended solids that can harbour and protect pathogenic bacteria and viruses from the oxidizing action of chlorine or ozone Carbon adsorption columns are preceded by filtration to prevent fouling of the granular activated carbon medium 3

4 2. Suspended solids removed through granularmedia filtration (UNEP., Water and Wastewater Reuse, 2008) 4

5 Tertiary wastewater treatment processes (Al-Malack, Water Supply and Wastewater Engineering, 2007 ) 5

6 A typical granular filter system (Shanahan, Water and Wastewater Treatment Engineering, 2006 ) 6

7 Typical layout of a biological treatment plant with tertiary granular-media filters (Viessman et al., Water Supply and Pollution Control, 2009 ) 7

8 Example 5-1 Four granular-media filters are designed for suspended-solids removal from a trickling-filter plant effluent. The average daily flow is 18.2 mgd (68,900 m 3 /d) and the maximum wet-weather flow for a 4-hr period is 31.0 mgd (117,000 m 3 /d). Data from a pilot-plant study are plotted in the figure followed. Filters are dual-media, gravity-flow beds, downtime for backwashing is 30 min, and water usage equals 150 gal/ft 2 (6.1 m 3 /m 2 ). Assume a nominal filtration rate of 3 gpm/ft 2 (54 m 3 /m 2 d), the inflow with SS of 30 mg/l and the outflow with SS of 5 mg/l. (1) Compute the area of granularmedia filters required for suspended-solids removal; (2) calculate the quantity of suspended solids removed from the filtration; and (3) check the peak rate with one filter cell out of service. 8

9 (Viessman et al., Water Supply and Pollution Control, 2009 ) 9

10 5.2 Dissolved organics removal 1. Dissolved organics left in wastewater after conventional treatments (Viessman et al., Water Supply and Pollution Control, 2009 ) 10

11 Tertiary wastewater treatment processes (Al-Malack, Water Supply and Wastewater Engineering, 2007 ) 11

12 2. Dissolved organics removed through granularcarbon adsorption (Shanahan, Water and Wastewater Treatment Engineering, 2006 ) 12

13 Contact time 7 to 20 minutes in typical water treatment plant A GAC tank (Shanahan, Water and Wastewater Treatment Engineering, 2006 ) 13

14 5.3 Pathogen removal 1. Pathogen left in wastewater after conventional treatments Many infectious diseases are transmitted by fecal wastes and the pathogens encompass all categories of microorganisms viruses, bacteria, protozoa and helminths Although disinfection (e.g., chlorination) is effective in killing bacteria and inactivating enteric viruses these pathogens can be protected in suspended and colloidal solids if the wastewater has not been filtered first for turbidity (solids) removal (Suspended and colloidal solids act as a shield for microorganisms from chlorine) Cysts of protozoa and helminth eggs are resistant to chlorine they need to be physically removed by effective chemical coagulation and granular-media or membrane filtration 14

15 2. Pathogen removal through chemical coagulationgranular media filtration-disinfection (UNEP., Water and Wastewater Reuse, 2008) 15

16 (Viessman et al., Water Supply and Pollution Control, 2009 ) 16

17 3. Pathogen removal through micro-ultra filtration Membrane filtrations can be classified, according to the size of materials removed, as followed Microfiltration (MF) membrane has pores of 0.1-1μm in diameter is effective against bacteria, cysts, and oocysts Ultrafiltration (UF) membrane has smaller pores ( μm) can remove particles and large molecules, including bacteria and viruses Nanofiltration (NF) membrane is similar to RO with lower operation pressure and salt rejection rate Reverse Osmosis (RO) membrane can remove even smaller ionic solutes such as salts resulting in almost mineralfree water, based on sieving and electrochemical interaction between molecules and membrane remove metal ions 17

18 (NanoSense., Nanofiltration, 2008) 18

19 (UNEP., Water and Wastewater Reuse, 2008) MF-UF membrane filtrations is a promising alternative technology for a large sedimentation pond or a coagulation process using chemicals filtering achieves the removal of bacteria and viruses contribute to minimizing health risk 19

20 Microfiltration (NanoSense., Nanofiltration, 2008) 20

21 Ultrafiltration (NanoSense., Nanofiltration, 2008) 21

22 Membrane filtration in Winsor Lake, St. John s (Niblock, Water Treatment Plants in St. John s, 2010 ) 22

23 Fully assembled rack in Winsor Lake at St. John s (Niblock, Water Treatment Plants in St. John s, 2010 ) 23

24 5.4 Toxic substance removal 1. Toxic water pollutants Numerous organic chemicals and several inorganic ions, mostly heavy metals are classified as toxic water pollutants A typical list of toxic pollutants heavy metals, cyanide, polynuclear aromatic hydrocarbons, aromatics, phenols, aliphatics, phthalates, pesticides Their toxicity to aquatic life related either to acute or chronic effects on the organisms or to humans by biological accumulation in seafood Their toxicity to humans related to either carcinogenicity or chromic disease through long term consumption of contaminants Currently over 100 substances are listed as priotity toxic water pollutants 24

25 2. Toxic substance left in wastewater after conventional treatments The general goal of municipal wastewater treatment with pretreatment of industrial wastewaters is to reduce the discharge of toxic pollutants to an insignificant level Heavy metals are partially removed by entrapment and adsorption onto settled solids or biological floc nevertheless, a portion appears in the effluent up tp 70% removal of Cd, Cr, Cu, Pb, Ni and Zn Organic toxic compounds maybe biologically decomposed or entrapped in settled solids or volatilized very little data are available on the removal rates 25

26 3. Toxic substance removed through nanofiltration (NanoSense., Nanofiltration, 2008) 26

27 Nanofiltration Typical pore size: micron (1 nm) Low to moderate pressure Removes toxic or unwanted bivalent ions (ions with 2 or more charges), such as Lead Nickel Mercury (II) Nanofiltration water cleaning serving Mery-sur-Oise, a suburb of Paris, France (NanoSense., Nanofiltration, 2008) 27

28 NanoCeram filters The active ingredient of the filter media is a nano alumina fiber, only 2 nm in diameter The nano fibers are highly electropositive Separate particles by charge, not size pores are large (2 microns) The filter retains all types of particles by electroadsorption including silica, natural organic matter, metals, bacteria, DNA and virus (NanoSense., Nanofiltration, 2008) 28

29 New nanomembranes -I Nanomembranes can be uniquely designed in layers with a particular chemistry and specific purpose insert particles toxic to bacteria Embed tubes that pull water through and keep everything else out signal to self-clean Image of a nanomembrane (NanoSense., Nanofiltration, 2008) 29

30 New nanomembranes -II Embed tubes composed of a type of chemical that strongly attracts ( loves ) water Weave into the membrane a type of molecule that can conduct electricity and repel oppositely charged particles, but let water through Water-loving tubes Electricity moving through a membrane (NanoSense., Nanofiltration, 2008) 30

31 4. Toxic substance removed through engineered wetlands Constructed wetlands (CWs) artificial designed and constructed utilize natural processes involving wetland vegetation, soils, and their associated microbial assemblages to assist in waste treatment satisfy the exponentially increasing demands of human expansion and resource exploitation Disadvantages of CWs performance inconsistent due to environmental changes e.g. wetland treatment efficiencies may vary seasonally in response to rainfall/drought and temperature chemical/biological components sensitive to toxic chemicals e.g. ammonia and pesticides flushes of pollutants may temporarily reduce treatment effectiveness 31

32 Water level above ground surface Water flow primarily above ground Surface Flow CWs Water level below ground Water flow through a sand/gravel bed Subsurface Flow CWs (Zhang et al., Phytoremediation in Engineered Wetlands, 2010) 32

33 Engineered wetlands (EWs) special and advanced kinds of CWs operating conditions are more actively monitored, manipulated and controlled all EWs CWs, but not all CWs EWs Five processes of phytoremediation in EWs Phytotransformation direct uptake of organic contaminants and metabolites into the plant tissue Rhizosphere bioremediation release of exudates and enzymes to stimulate microbial activity and the resulting biodegradation of organics in the rhizosphere Phytoextraction uptake and recovery of metals into above-ground biomass Rhizofiltration filter metals from water onto root systems Phytostabilization stabilize wastes by erosion control and evapotranspiration of large quantities of water 33

34 Design modifications Process additions Vegetation changes Ways to "Engineer" a Constructed Wetland Advanced operation methods Aeration in/under substrate beds to increase aerobic biodegradation rates Use of engineered SSF substrates in place of gravel to adsorb contaminants and control hydraulic loading Chemical and energy addition (eg. low grade heat) Alkaline streams Plant harvesting for nutrient removal Phytoremediating plants, stress resistant species Recycle of effluents, intermediate streams Separation of competing reactions into different cells (Zhang et al., Phytoremediation in Engineered Wetlands, 2010) 34

35 Source: Suthersan, 1997 Phytotransformation and rhizosphere bioremediation of organic contaminants by plants in EWs 35

36 Phytoextraction of heavy metals in EWs Source: Suthersan,

37 Appleton/Glenwood EW Treatment System in NL (Zhang et al., Phytoremediation in Engineered Wetlands, 2010) 37