Combined Schemes; Pros & Cons, or, “when to use”? Christos Anastasiou, PhD Department of Civil & Environmental Engineering Faculty of Engineering & Architecture MEDAWARE

Outline “Definition” of a “Combined Scheme” Combination of Treatment Methods Co-treatment of Wastewaters Centralized vs. Decentralized Systems Treatment Technologies (advantages/disadvantages)

What is a “combined scheme”? Combined Sewerage Systems (Combined Overflow Systems) ? Combination of Unit Processes and Treatment Methods? Combination of Waste Streams (Co-treatment) ? Centralized vs. Decentralized Treatment Systems?

Sanitary sewer systems may either exist separate from storm-water sewers, or a single set of pipes may be used to carry both types of wastewater in a combined sewer system. Old technology (prior 1960’s) – Combined systems are no longer built, but still exist in many communities.  Combined sewer systems typically bypass part of the flow during periods of high runoff. What is a “combined scheme”? Combined Overflow Systems

Conventional Treatment Unit Processes & Methods Physical/Chemical Processes  Dilution, screening, mixing, flocculation, sedimentation, flotation, aeration, filtration, precipitation, coagulation, chemical oxidation, chemical stabilization. Biological Methods  Suspended (e.g. AS, oxidation ditch, SBR) & attached growth (e.g. trickling filters, RBC) aerobic, anaerobic suspended & attached growth (e.g. CSTR, PFR, UASB, packed reactors).

Advanced Treatment Unit Processes & Methods Filtration processes (i.e. depth, surface, micro & ultrafiltration, and reverse osmosis) Electrodialysis Adsorption Gas Stripping Ion Exchange Advanced Oxidation Processes - chemical Distillation

Why do we need to use Advanced Treatment? To achieve further organics and TSS treatment to meet more stringent standards or to allow for better disinfection To remove more nutrients (beyond what conventional methods allow) To remove specific organic and inorganic constituents Basically,  Wastewater Constituents: Conventional, non-conventional, and emerging  Conventional Treatment for Conventional Constituents AND Advanced Treatment for Non-conventional Constituents (Emerging constituents removal occurs in both but not well quantified)

1 = 50% Potential for Contaminant Removal of various Unit Processes and Operations ConstituentPrimaryASBNR Trickling Filter Coag. Floc-Sed. Activated Carbon Filtration (after AS) RO BOD/COD TSS Nitrogen Phosphorus Alkalinity223 Total Coliform TDS3 Turbidity TOC

Combination of Unit Processes or Treatment Methods Why Combine Methods?  Complete abatement of pollutants cannot be achieved by a single process for certain waste streams Example: Combined Aerobic Treatment Processes (i.e. Coupling of Trickling Filter and Activated Sludge treatments) are often used to  Upgrade an existing AS system  Reduce the strength of WW, if we have a combination of industrial & domestic waste  To protect a nitrification AS process from toxic or inhibitory substances

Necessity of Combination of Treatment Methods Example: Olive Oil Wastewater Some characteristics of the wastewater: high organics, high BOD:N:P ratio, low pH, high conductivity, high polyphenols – toxic, high SS) Treatment Capital Cost ($/m 3 day) Energy required (kWh/m 3 ) Drawbacks Combustion5, Destruction of recoverable organics Single effect distillation11, Post-treatment of distillate (~2.5Kg COD/m 3 day) Activated Sludge20,00030 Dilution water. Nutrients Addition. Sludge Disposal Trickling Filters10,00015 (as Activated Sludge) Anaerobic Degradation4,000<1 Dilution water. Long start-up

Necessity of Combination of Treatment Methods Example: Animal Waste Barham Farm (4000 swine), North Carolina, USA Ambient Temperature Anaerobic Digester (with energy production); Nitrification Tanks; Old Anaerobic Lagoon (denitrification); Greenhouses.

Necessity of Combination of Treatment Methods Example: Animal Waste Anaerobic Digester Nitrification Tanks Greenhouses Sprayfield

Necessity of Combination of Treatment Methods more examples Slaughterhouse waste Landfill Leachate etc. Nevertheless, The simplest possible method is still desirable!!

What is a “combined scheme”? Combination of Waste Streams (co-treatment) Why combine waste streams?  Convenience, for example Quantity of waste streams (economies of scale) Proximity of waste sources to one another  Enhancement of treatment, for example to balance the pH To add necessary nutrients

What is a “combined scheme”? Combination of Waste Streams (co-treatment) Examples  Animal Waste & Organic Solid Waste  Municipal Wastewater & Landfill Leachate  Municipal Wastewater & Organic Solid Waste  Various Industrial Wastewaters Example: Ypsonas Industrial Effluent Treatment Plant (Limassol, Cyprus) – wastewater received from  Potato chip factory  Aluminum processing  Textile factory  And others…

What is a “combined scheme”? Centralized vs. Decentralized Treatment Systems Current “conventional” practice:  Design of larger treatment systems (>3500 m 3 /day) Capture of economies of scale However, small or rural communities have different characteristics and needs  Bringing wastewater from many small sources to one single location for treatment may not always be the best option.

Decentralized Treatment Systems WHERE to consider (according to USEPA) ? Where the operation and management of existing onsite systems must be improved Where individual onsite systems are failing and the community cannot afford the cost of a conventional wastewater management system Where the community or facility is remote from existing sewers Where localized water reuse opportunities are available Where fresh water for domestic supply is in short supply Where existing wastewater treatment plant capacity is limited and financing is not available for expansion Where, for environmental reasons, the quantity of effluent discharged to the environment must be limited Where the expansion of the existing wastewater collection and treatment facilities would involve unnecessary disruption to the community Where the site or environmental conditions that require further wastewater treatment or exportation of wastewater are isolated to certain areas Where residential density is sparse Where regionalization would require political annexation that would be unacceptable to the community Where specific wastewater constituents are treated or altered more appropriately at the point of generation

Decentralized Treatment Systems WHAT to consider? Reliable, stable and robust process Simple operation & management Minimal or no need of chemicals Minimal or no need of external power supply Local availability of spares

Typical wastewater treatment options for small and decentralized systems Wetland in Thessaloniki, Greece Aerated lagoon system, USA Schematic of Septic Tank

Technologies for the Treatment of Wastewater Some final words… Each situation is different and needs to be given dual consideration, different alternatives exist for each system from small scale households to large scale centralized one. Nevertheless, there is a clear trend toward intensive treatment technologies (a trend that is exacerbated by the preference of engineering consultants and contractors). Instead, more attention should be given, where appropriate, to properly designed lower-cost, simpler to operate processes as well as to decentralized technologies. These should be adopted depending on the influent wastewater and on the desired effluent quality. Also, whenever feasible, a reuse component should be included for all new wastewater treatment projects

END OF PRESENTATION

Constituents in Reclaimed Water Conventional (measured in mg/L; used in designing conventional WWTPs)  TSS  BOD; COD  TOC  Nitrogen (Ammonia; Nitrate; Nitrite)  Phosphorus  Microorganisms: Bacteria; Viruses ; Protozoan cysts & oocysts Non-conventional (to be removed or reduced by advanced treatment processes)  Refractory organics  VOC  Surfactants  Metals  TDS Emerging (measured in μg/L; long-term health concerns possible; not easy to remove)  Pharmaceuticals  Antibiotics (veterinary & human)  Home-care, industrial, and household products  Hormones (steroids) and Endocrine Disrupters