AANAEROBIC TREATMENT AS A NAEROBIC TREATMENT AS A SUSTAINABLE TREATMENT OPTION FOR SUSTAINABLE TREATMENT OPTION FOR DOMESTIC WASTEWATER AND ORGANIC DOMESTIC WASTEWATER AND ORGANIC FRACTION OF MUNICIPAL SOLID WASTEFRACTION OF MUNICIPAL SOLID WASTE

Prof. Dr. Izzet OzturkProf. Dr. Izzet Ozturk

Istanbul Technical University, Environmental Engineering Faculty, Istanbul Technical University, Environmental Engineering Faculty, 34469, Maslak, Istanbul/TURKEY34469, Maslak, Istanbul/TURKEY

High-rate anaerobic treatment has High-rate anaerobic treatment has been used widelybeen used widely for the treatment of for the treatment of many industrial and municipal wastewatersmany industrial and municipal wastewaters in the last decades in the last decades

Benefits Drawbacks

1. Efficient in the removal of organic material especially for tropical regions (developing countries)

1. Long start-up period when seed sludge is not available, as the growth rate of methanogenic microorganisms is low

2. Low construction cost and small land requirements as generally at temperatures > 20˚C and high loading rates can be applied

2. Low pathogen removal

3. Low operation and maintenance costs, energy consumption is low and little equipment is needed

3. Requirement for post treatment to reach the effluent standarts

4. Lower sludge production as compared to aerobic and physical-chemical treatment processes

4. Low removal efficiently of particulate organic material at low temperatures

5. Biogas production which can be used for energy production

5. Risk for odour nuisance from the reduction of sulphate to sulphide

Table 1. The benefits and drawbacks of anaerobic treatment of domestic sewage in the high-rate anaerobic systems

Under suitable conditions in an anaerobic sewage treatment system a bacterial population will develop that is compatible with the applied Under suitable conditions in an anaerobic sewage treatment system a bacterial population will develop that is compatible with the applied hydraulic and organic loads. Among the factors that determine the removal efficiency of biodegradable organic matter, the following are hydraulic and organic loads. Among the factors that determine the removal efficiency of biodegradable organic matter, the following are important: important:

1) The nature of the anaerobic matter to be removed1) The nature of the anaerobic matter to be removed

2) The suitability of environmental factors for anaerobic digestion2) The suitability of environmental factors for anaerobic digestion

3) The retained amount of viable bacterial matter3) The retained amount of viable bacterial matter

4) The intensity of contact between the influent organic matter and the bacterial populations4) The intensity of contact between the influent organic matter and the bacterial populations

5) The design of the anaerobic reactor5) The design of the anaerobic reactor

6) The retention time of sewage6) The retention time of sewage

Important environmental factors affecting anaerobic sewage digestion are:Important environmental factors affecting anaerobic sewage digestion are:

- temperature- temperature

- pH- pH

- the presence of essential nutrients- the presence of essential nutrients

- the absence of excessive concentrations of toxic compounds- the absence of excessive concentrations of toxic compounds

Nutrients (both macronutrients, nitrogen and phosphorus, and micronutrients) are abundantly available in sewageNutrients (both macronutrients, nitrogen and phosphorus, and micronutrients) are abundantly available in sewage

Compounds that could exert a distinct toxic influence on the bacterial population as well as sulphide are generally absent in sewageCompounds that could exert a distinct toxic influence on the bacterial population as well as sulphide are generally absent in sewage

Besides type of the sewerage system (combined or seperate) also affects the composition of sewage as well as anaerobic treatment efficiencyBesides type of the sewerage system (combined or seperate) also affects the composition of sewage as well as anaerobic treatment efficiency

High-rate anaerobic systems are generally applied in the temperature range High-rate anaerobic systems are generally applied in the temperature range ofof 25-40 25-40CC

However, many recent researches conducted at all temperature conditions revealed that temperature is not a limiting factor in However, many recent researches conducted at all temperature conditions revealed that temperature is not a limiting factor in anaerobic treatment applications if the appropriate process design is chosenanaerobic treatment applications if the appropriate process design is chosen

When they are operated in lower temperature rangesWhen they are operated in lower temperature ranges ( (5-205-20CC)), various adaptations of the conventional high-rate reactor design are , various adaptations of the conventional high-rate reactor design are neededneeded

The methanogenic biomass and the wastewater should be in sufficient contactThe methanogenic biomass and the wastewater should be in sufficient contact ( (can be achieved by increased liquid upflow velocitiescan be achieved by increased liquid upflow velocities))

• Psychrophilic anaerobic treatment is an attractive Psychrophilic anaerobic treatment is an attractive option for wastewaters which are discharged at option for wastewaters which are discharged at moderate to low temperatures moderate to low temperatures ((optimal temperature optimal temperature for psychrophilic microorganisms is around 17for psychrophilic microorganisms is around 17CC))

• Since domestic sewage has a temperature lower Since domestic sewage has a temperature lower than 35than 35C, heating is required during the mesophilic C, heating is required during the mesophilic anaerobic treatment. Thus, anaerobic treatment anaerobic treatment. Thus, anaerobic treatment systems allow substantially lower treatment costs due systems allow substantially lower treatment costs due to their ability to operate at low temperatures (10-to their ability to operate at low temperatures (10-2020C)C)

• IIn recent years anaerobic treatment of wastewaters n recent years anaerobic treatment of wastewaters having low COD concentrations could be efficient having low COD concentrations could be efficient especially with high-rate reactors such as UASB and especially with high-rate reactors such as UASB and fluidized bed reactorsfluidized bed reactors

• Since low COD concentration of the influent results Since low COD concentration of the influent results in very low substrate levels, low biogas productions in very low substrate levels, low biogas productions will occur inside the reactor as wellwill occur inside the reactor as well ( (HRT determineHRT determiness the reactor volumethe reactor volume))

The most appropriate anaerobic system to treat domestic wastewater has been considered as the UASB reactor because of its simplicity, The most appropriate anaerobic system to treat domestic wastewater has been considered as the UASB reactor because of its simplicity, low investment and operation costslow investment and operation costs

Particulate organics are physically removed due to settling, adsorption and entrapment which is the first step in the anaerobic treatment Particulate organics are physically removed due to settling, adsorption and entrapment which is the first step in the anaerobic treatment and conversion of domestic sewageand conversion of domestic sewage

The rate-limiting step in the overall digestion process is the hydrolysis of retained particulates which need relatively long retention times, The rate-limiting step in the overall digestion process is the hydrolysis of retained particulates which need relatively long retention times, depending on the applied process temperaturedepending on the applied process temperature

Direct anaerobic treatment of domestic sewage is generally not applied because of the fact that the high SS concentration in sewage causes considerable difficultiesDirect anaerobic treatment of domestic sewage is generally not applied because of the fact that the high SS concentration in sewage causes considerable difficulties

Under low temperature conditions, the SS are hydrolysed very slowly and tend to acccumulate in the reactorUnder low temperature conditions, the SS are hydrolysed very slowly and tend to acccumulate in the reactor (deteriorate the granular sludge) (deteriorate the granular sludge)

IIn order to guarantee an efficient treatment of domestic sewage under low temperature conditions, at least part of the SS present in the wastewater should be n order to guarantee an efficient treatment of domestic sewage under low temperature conditions, at least part of the SS present in the wastewater should be removed before feeding the wastewater to a sludge bed reactorremoved before feeding the wastewater to a sludge bed reactor

On the other hand, it was reported that two stage systems are more suitable for anaerobic sewage treatment at low temperatures whereas at high temperatures single On the other hand, it was reported that two stage systems are more suitable for anaerobic sewage treatment at low temperatures whereas at high temperatures single stage systems should be chosenstage systems should be chosen

At two stage reactor approach generally long HRT’s are applied for SS hydrolysis at the first stage whereas short HRT’s are enough for methane production at the At two stage reactor approach generally long HRT’s are applied for SS hydrolysis at the first stage whereas short HRT’s are enough for methane production at the second stagesecond stage

SSpecific biogas production rate is relatively low under psychrophilic conditionspecific biogas production rate is relatively low under psychrophilic conditions ::

- - At low temperatures, the increase of COAt low temperatures, the increase of CO22 dissolution in water might cause a decrease in the pH of the dissolution in water might cause a decrease in the pH of the

reactor because the solubility of gaseous compounds present in biogas increases with decrease in reactor because the solubility of gaseous compounds present in biogas increases with decrease in temperaturetemperature

- Low biodegradable organic matter concentration in the influent- Low biodegradable organic matter concentration in the influent

Pilot and full-scale UASB reactor applications for domestic sewage are given in Table 2

Country Volume(m3)

˚C Influent (mg/L)

Seed h

(hr)

Removal(%)

Reference

COD BOD SS COD BOD SS

Holland 6 10-18 100-900

53-474 10-700*

Granular 9-16 46-60 42-48 55-75 de Man et al., 1986

Holland 20 11-19 150-550

43-157 50-400*

Granular 6.2-18

31-49 23-46 (-) de Man et al., 1986

Holland 120 >13 391 291 (-) Granular 2-7 16-34 20-51 (-) van der Last and Lettinga, 1992

Colombia 64 25 267 95 (-) Digested cow

manure

6-8 75-82 75-93 70-80 Lettinga et al., 1987

Colombia 3360 24 380 160 240 None 5 45-60 64-78 60 Schellinkhout and Osorio, 1994

Italy 336 7-27 205-326

55-153 100-250

None 12-42 31-56 40-70+ 55-80+ Collivignarelli et al., 1991; Maaskant et al., 1991

India 1200 20-30 563 214 418 None 6 74 75 75 Draaijer et al., 1992

India 12000 18-32 1183 484 1000 (-) 8 51-63 53-69 46-64 Haskoning, 1996a; Tare et al., 1997

India 6000 18-32 404 205 362 (-) 8 62-72 65-71 70-78 Haskoning, 1996b; Tare et al., 1997

Brasil 120 18-28 188-459

104-255

67-236

Granular 5-15 60 70 70 Vieira and Garcia, 1992

Brasil 477 (-) 600 (-) 303 Non-adapted

13 68 (-) 76 Chernicharo andBorges, 1997

Table 2. Pilot and full scale UASB reactor applications for domestic sewage”

Wastewaters are usually transported to centralised treatment plants through extended sewage networks however, decentralised wastewater treatment, Wastewaters are usually transported to centralised treatment plants through extended sewage networks however, decentralised wastewater treatment, i.e. community – or house- on-site treatment, may be more sustainable in some casesi.e. community – or house- on-site treatment, may be more sustainable in some cases

Anaerobic on-site treatment is considered sustainable with its simple, thus cost-effective reactor design, small space requirement, low sludge Anaerobic on-site treatment is considered sustainable with its simple, thus cost-effective reactor design, small space requirement, low sludge production, low energy and nutrient demand, potential for energy production, high loading capacity, efficient removal of organic matter, possibility for production, low energy and nutrient demand, potential for energy production, high loading capacity, efficient removal of organic matter, possibility for nutrient recycling and suitability for small housesnutrient recycling and suitability for small houses

The produced biogas is collected and utilised as renewable energyThe produced biogas is collected and utilised as renewable energy

Simple and easy-to-use anaerobic processes suitable for on-site treatment are septic tank, UASB-septic tank, and accumulation systemSimple and easy-to-use anaerobic processes suitable for on-site treatment are septic tank, UASB-septic tank, and accumulation system

On-site Anaerobic On-site Anaerobic TreatmentTreatment

Figure 1. Flow scheme for a decentralised integrated system. 1. Pre-sedimentation tank, 2. UASB reactor, 3. RBC = Rotating Biological Contact Reactor, 4. UV/O3 = ultraviolet-ozone generator

Figure 2. Flow diagram for an anaerobic on-site treatment

Anaerobic treatment is effective in removing biodegradable Anaerobic treatment is effective in removing biodegradable organic compounds, leaving mineralized compounds like organic compounds, leaving mineralized compounds like ammonium, phosphate and sulfur in the solution. ammonium, phosphate and sulfur in the solution.

These compounds therefore have to be removed by an These compounds therefore have to be removed by an additional post-treatment step to meet sufficiently the criteria additional post-treatment step to meet sufficiently the criteria for a sustainable environmental protection. for a sustainable environmental protection.

Besides it was reported that no pathogen removal could be Besides it was reported that no pathogen removal could be achieved at low temperatures. Thus, anaerobic treatment of achieved at low temperatures. Thus, anaerobic treatment of low strength wastewaters by UASB reactor should be low strength wastewaters by UASB reactor should be considered as a pre-treatment alternativeconsidered as a pre-treatment alternative

Post-Treatment AlternativesPost-Treatment Alternatives

Figure 3. Sectional view of a UASB + duckweed ponds Figure 3. Sectional view of a UASB + duckweed ponds + fish pond system+ fish pond system

UASB

Biogas

Sludge to drying beds

StabilizationPond

To land

UASB

Biogas

Sludge to drying beds

Facultative Aerated Lagoon

To river or land

UASB

Biogas

Sludge to drying beds

Three ChamberOxidation

Pond

To land

(a)

(b)

(c)

Figure 4. Treatment alternatives following UASB reactor (a) Stabilization pond (b) Facultative aerated lagoon (c) Oxidation pond

Anaerobic Digestion of Anaerobic Digestion of OFMSWOFMSW

Anaerobic digestion for the treatment of OFMSW was devoloped in Anaerobic digestion for the treatment of OFMSW was devoloped in the 1980’s and early 1990’s. the 1980’s and early 1990’s.

The biomethanization of OFMSW will become a very feasible option The biomethanization of OFMSW will become a very feasible option by applying subsidies to electricity production from wastes.by applying subsidies to electricity production from wastes.

In most of the In most of the EU member countriesEU member countries the electricity generated from the electricity generated from the reneweable sources is subsided with an the reneweable sources is subsided with an additional Є0,1/kWh additional Є0,1/kWh

Since 1990, more than 120 waste treatment facilities have been Since 1990, more than 120 waste treatment facilities have been constructed in Europe.constructed in Europe.

In most of these plants, the anaerobic digestion is followed by an In most of these plants, the anaerobic digestion is followed by an aerobic phase, for the additional pathogen removal, so that not only aerobic phase, for the additional pathogen removal, so that not only biogas but also compost is produced. biogas but also compost is produced.

The nutrient rich supernatant from these digesters can be treated The nutrient rich supernatant from these digesters can be treated with MAP and struvite is produced which has a marketing value as a with MAP and struvite is produced which has a marketing value as a fertilizer (Also the supernetant from digesters has a potential of fertilizer (Also the supernetant from digesters has a potential of agricultural use).agricultural use).

Waste CharacteristicsWaste Characteristics The organic fraction of municipal solid waste is rather a The organic fraction of municipal solid waste is rather a

heterogenous substrate and heterogenous substrate and the biogas yield in the biogas yield in anaerobic treatment of OFMSW is dependent not only anaerobic treatment of OFMSW is dependent not only the the proces configuration, but also on the waste the the proces configuration, but also on the waste characteristicscharacteristics..

The waste characteristics is highly dependent on the The waste characteristics is highly dependent on the collection systemcollection system..

Source sorting of MSW generaly provides OFMSW of Source sorting of MSW generaly provides OFMSW of higher quality in terms of biogas yield and smaller higher quality in terms of biogas yield and smaller quantities of non-biodegradable contaminants like plastics.quantities of non-biodegradable contaminants like plastics.

Mechanically seperated OFMSW which has a lower biogas Mechanically seperated OFMSW which has a lower biogas potential is more contaminated, which leads to persistent potential is more contaminated, which leads to persistent handling problems and lower acceptability of the effluent handling problems and lower acceptability of the effluent product of the treatment process as fertilizer on product of the treatment process as fertilizer on agricultural land.agricultural land.

Waste Characteristics and Biogas Waste Characteristics and Biogas PotentialPotential

Substrate TypeSubstrate TypeBB00

(m(m33 CH CH44/kg TVS)/kg TVS)GG00

(m(m33/kg TVS)/kg TVS)

Mechanicaly Sorted OFMSW Mechanicaly Sorted OFMSW (MS-OFMSW)(MS-OFMSW) 0,16 - 0,370,16 - 0,37 0,29 - 0,660,29 - 0,66Separetely Collected OFMSW Separetely Collected OFMSW (SC-OFMSW)(SC-OFMSW) 0,45 - 0,490,45 - 0,49 0,81 - 0,890,81 - 0,89Source Sorted OFMSW Source Sorted OFMSW (SS-OFMSW)(SS-OFMSW) 0,37 - 0,400,37 - 0,40 0,67 - 0,720,67 - 0,72

B0 : Maximum Methane Potential, G0 : Maximum Biogas Potential (%55 CH4)

ParameterParameter

Mechanicaly Sorted Mechanicaly Sorted OFMSW OFMSW

(MS-OFMSW)(MS-OFMSW)

Source Sorted Source Sorted OFMSW OFMSW

(SS-OFMSW)(SS-OFMSW)TS (g/kg)TS (g/kg) 647,2647,2 163,9163,9

TVS (%TKM)TVS (%TKM) 46,546,5 90,690,6

TCOD TCOD (kgO(kgO22/kg)/kg) 0,50,5 1,11,1

TKN (%TS)TKN (%TS) 1,41,4 2,12,1

P (%TS)P (%TS) 1,91,9 2,12,1

Co-digestion ApproachCo-digestion Approach The co-digestion concept involves the treatment of several The co-digestion concept involves the treatment of several

waste types in a single treatment facility. waste types in a single treatment facility.

The profit of co-digestion in the anaerobic degredation proces The profit of co-digestion in the anaerobic degredation proces is mainly within the folloving areas:is mainly within the folloving areas:

Increasing the methane yield Increasing the methane yield Improving the process stabilityImproving the process stability Achieving a better management of wasteAchieving a better management of waste The economical benefits of the collection and treatment of different The economical benefits of the collection and treatment of different

types of wastes in a single treatment facility (Figure 5)types of wastes in a single treatment facility (Figure 5) The fermentation products of OFMSW which is mainly VFA can be The fermentation products of OFMSW which is mainly VFA can be

used as external carbon source for biological nutrient removal plants used as external carbon source for biological nutrient removal plants which suffers from organic carbon deficiency (Figure 5)which suffers from organic carbon deficiency (Figure 5)

Cake to Post Aerobic

Composting

FiltrateLiquid Fertilizer

Seperate Collected

Organic Fraction of Municipal Solid Waste

(SC-OFMSW)

A general flow scheme for the implementation of co-digestion aproach and anaerobic treatment of municipal wastewater in a single treatment facility

Qgas=0.1-0.3 m3/kg CODremoved

(80% CH4)

Liquid Fermentation Products (High VFA)

OFMSW ~ 8 to 10% TS

Plastics & Paper

Qgas=0.30 m3/kg VSfed

(65-70% CH4)

Biogas II

Biogas I

Methane Reactor

PumpDomestic Wastewater

Grit ChamberScreen

UASB Reactor

Aerated or SBR Lagoon

Size Reduction

Agricultural Use

Solar Energy Assisted Heating (if required!)

Heavy Fractions

Pulper

Anaerobic Hdrolysis & Acid

Fermentation

Sludge Dewatering

Co-digestion Approach The application of anaerobic co-digestion process may face

problems due to some substrate characteristics.

High total solids content of typically 30 – 50% High C:N ratio Deficiecy in macro- and micronutrients Content of toxic compounds (heavy metals, phthalates)

The key for codigestion lies in balancing several parametres in the co-substrate mixture.

Waste BWaste A

Makro and micro nutrientsC:N ratio

pHInhibitors/toxic compounds

Biodegradable organic matterDry matter

Co-digestion with Sewage SludgeCo-digestion with Sewage Sludge

The codigestion can be applied at existing facilities without The codigestion can be applied at existing facilities without great investments and it combines the treatment of the two great investments and it combines the treatment of the two largest municipal waste streams.largest municipal waste streams.

The addition of high solids concentration of OFMSW digester The addition of high solids concentration of OFMSW digester operated with sludge having a low TS concentration will be operated with sludge having a low TS concentration will be possible even in rather high concentrationspossible even in rather high concentrations

The stabilizing effect of sludge on the digestion of OFMSW The stabilizing effect of sludge on the digestion of OFMSW has been confirmed with sludge doses between 8 – 20% of has been confirmed with sludge doses between 8 – 20% of feedstock volatile solids (Kayhanian and Rich, 1996; Rivard feedstock volatile solids (Kayhanian and Rich, 1996; Rivard et al., 1990). et al., 1990).

For the codigestion of OFMSW with sewage sludge, the For the codigestion of OFMSW with sewage sludge, the optimum C:N ratio of the feedstock was found to be in the optimum C:N ratio of the feedstock was found to be in the range of 25 to 30 based on biodegradable carbon (Kayhanian range of 25 to 30 based on biodegradable carbon (Kayhanian and Tchobanoglolous, 1992; Kayhanian and Rich, 1996). and Tchobanoglolous, 1992; Kayhanian and Rich, 1996).

Co-digestion with Other Waste Co-digestion with Other Waste TypesTypes

Other organic waste types such as; Other organic waste types such as;

Livestock waste (manure)Livestock waste (manure) Olive mill effluents Olive mill effluents MacroalgaeMacroalgae Wastes generated by agro industries such as Wastes generated by agro industries such as

slaughterhouses, meat-processing industriesslaughterhouses, meat-processing industries

can also be used as a co-substrate with can also be used as a co-substrate with OFMSW.OFMSW.

THANK YOU FOR THANK YOU FOR YOUR ATTENTION!YOUR ATTENTION!