Summary

Table 1.6 summarizes the effect, advantages and disadvantages of the various processes presented in this volume for the removal of nitrogen from waste water. The effect that each process has on each of the three major forms of nitrogen, organic nitrogen, ammonium and nitrate are shown. Average removal percentages which can be expected from the different processes are also indicated.

Table 1.7 shows an estimation of costs for the different processes compared with the efficiency. The processes are divided into three categories; expensive, moderate and low cost processes, because it is difficult to estimate exact figures. Also, the efficiency is divided into low, medium and high content of nitrogen in the influent waste water.

The overall removal in a particular treatment plant will depend on the types of unit processes employed and their relation to each other.

In general, the reliability of a given treatment process is higher for the physico-chemical treatment processes than for the biological treatment processes.

On the other hand, costs are generally higher for the physico-chemical methods than for the biological methods. It is, therefore, important to find a balance between costs and reliability for the process, used for each of the types of waste water. This can only be found by conducting pilot-plant studies of the specific waste water before deciding which application is to be used.

Table 1.6 The effect, advantages and disadvantages of various treatment processes on nitrogen compounds

Effect on nitrogen form

Removal

Process

Process Reference

Treatment process

Organic N NH3/NH4*

no3-

of total nitrogen entering process %

Advantages

Disadvantages Chapter

Biological treatment

Processes

Attached-growth processes

- Nitrification

(separate stage)

Limited effect ->N03"

No effect

70-90

Good protection against most toxicants. Stable operation. Stability not linked to secondary clarifier as organisms are attached to media.

Greater number of 5 unit processes required than for combined carbon oxidation and nitrification.

Nitrification

(combined oxidation

and nitrification)

Limited effect ~»N03'

No effect

5-20

Combined treatment of carbon and ammonia in a single stage not linked to a secondary clarifier as biomass attached to media

No protection against 5 toxicants. Only moderate stability of operation.

Cold weather operation impracticable in most cares.

Effect on nitrogen form

Treatment process

Organic N NH/NH/ NOs process %

Denitrification using methanol No effect No effect 80-90% removal following a nitrification stage.

Simultaneous nitrification and denitrification (SND). No effect ->N03" ->N2

Removal Process Process Reference of total Advantages Disadvantages Chapter nitrogen entering

70-95

Denitrif ¡cation rapid; demonstrated stability of operation; stability not linked to clarifier as organisms on media. High degree of nitrogen removal possible.

Methanol required. Greater number of unit processes required for nitrifi-cation/denitrifica-tion than in combined systems.

60-80 Conversion of ammonium to gaseous nitrogen. Rapid nitrogen removal compared with suspended cultures.

Low space required for application.

Still only possible on pilot plant scale. Fluctuation in stability. Very sensitive to high BOD5 in influent.

Treatment process

Effect on nitrogen form Organic N NHJNH/

Combined carbon oxidation nitrification/denitrification in suspended-growth reactor using endogenous carbon source.

No effect

No effect

80-90% removal

Combined carbon oxidation No nitrification/denitrification in suspended-growth reactor using waste water carbon source.

No effect 80-90% removal

Removal Process Process Reference of total advantages disadvantages Chapter nitrogen entering process %

5-20 No methanol required;

lesser number of unit processes required; better control of filamentous organisms in activated-sludge process possible; single basin can be used; adaptable to sequencing batch reactor; process can be adapted to include biological phosphorus removal.

Denitrification occurs at 6

very slow rates; longer detention time and much larger structures required than methanol-based system; stability of operation linked to clarifier for biomass return; difficult to optimize nitrification and denitrification separately; biomass requires sufficient dissolved-oxygen level for nitrification to occur; less nitrogen removal than methanol based system.

5-20

No methanol required: lesser number of unit processes required; better control of filamentous organisms in activated-sludge process possible; single basin can be used; adaptable to sequencing batch reactor; process can be adapted to include biological phosphorus removal.

Denitrification occurs at slow rates, longer detention time and larger structures required than methanol-based system; stability of operation linked to clarifier for biomass return; difficult to optimize nitrification and denitrification separately: biomass requires sufficient dissolved-oxygen level for nitrification to occur less nitrogen removal tin an methanol-based system.

Effect on nitrogen form

Treatment process

Organic N NH^NH/ N03

Suspenced-growth denitrifi- No effect No effect 80-90% cients using methanol removal following a nitrification stage.

Bacterial assimilation

No effect 40-70% Slight removal

Removal of total nitrogen entering process %

Process advantages

Process disadvantages

70-95

Denitrification rapid; small structures required; demonstrated stability of operation; few limitations in treatment sequence options; exess methanol oxidation step can be easily incorporated; each process in system can be separately optimized; high degree of nitrogen removal possible.

Reference Chapter

Methanol required; stability of operation linked to clarifier for biomass return; greater number of unit processes required for nitrification/den itrification than in combined systems.

30-70

Effect on nitrogen form

Treatment process

Organic N NHJNH4+ NOs'

Denitrification using methanol No effect No effect 80-90% removal following a nitrifica-cation stage.

Simultaneous nitrification and denitrification (SND). No effect ->N03" ->N2

Removal Process of total Advantages nitrogen entering process %

Process Reference

Disadvantages Chapter

70-95

Denitrification rapid; demonstrated stability of operation; stability not linked to clarifier as organisms on media. High degree of nitrogen removal possible.

Methanol required. Greater number of unit processes required for nitrification/denitrification than in combined systems.

60-80 Conversion of ammonium to gaseous nitrogen. Rapid nitrogen removal compared with suspended cultures.

Low space required for application.

Still only possible on pilot plant scale. Fluctuation in stabi-Very sensitive of high BOD5 in influent.

Effect on-nitrogen form

Treatment process

Organic N NHj/NH/ N03

Suspended growth processes

-Nitrification

(separate stage) Limited effect —>N03" No effect

-Nitrification (combined oxidation and nitrification). Limited effect ->N03" No effect

Removal Process Process Reference of total advantages disadvantages Chapter nitrogen entering process %

70-90 Good protection against most toxicants. Stable operation. Low effluent ammonia possible.

Sludge inventory requires careful control when BOD5/TKN ratio is low. Stability of operation linked to operation of secondary clarifier for biomass return.

5-20 Combined treatment of carbon and ammonia in a single stage. Inventory control of mixed-liquor due to high BOD5/TKN ratio.

No protection against toxicants. Only moderate stability linked to operation of secondary clarifier for biomass return. Large reactors required in cold weather.

Effect on nitrogen form

Treatment process

Organic N NH3/NH4* NOj

Physical and chemical treatment processes.

Air stripping (Air) No effect 60-95% No effect removal

CO 03

Ramoval of total nitrogen entering process %

Process advantages

Process disadvantage

Reference Chapter

Process can be controlled for selected ammonia removals. Most applicable if required seasonally in combination with lime system for phosphorus removal. Process may be able to meet total nitrogen standards. Not sensitive to toxic substances.

Process is senitive to temperature. Ammonia solubility increases with lower temperatures. Air requirements also vary. Fogging and icing occur in cold weather. Ammonia reaction with sulphur dioxide may cause air pollution problems. Process usually requires lime for pH control, thereby increasing treatment cost and lime-related operating and maintenance problems. Carbonate scaling of packing and piping. Potential noise and aesthetic problems.

Treatment process

Effect on nitrogen form Organic N NH3/NH4* NO3

Break-point chlorination

Uncertain

90-100% removal

No effect

Removal Process Process Reference of total advantages disadvantages Chapter nitrogen entering process %

80-95

With proper control, aH ammonia nitrogen can be oxidized. Process can be used folowing other nitrogen removal processes for line tuning of nitrogen removal. Concurrent effluent disinfection. Limited space requirement. Not sensitive to toxic substances and temperature. Low capital costs. Adaptable to existing facility.

May produce high chlorine residuals that are toxic to aquatic organisms. Wastewater contains a variety of chlorine-deman-ding substances which increase cost of treatment. Process is sensitive to pH, which affects dosage requirements.

Trihalomethane formation may impact quality of water supplies. Addition of chlorine raises effluent TDS. Process may not be able to meet total nitrogen standards. Requires careful control of pH to avoid.for-mation of nitrogen trichloride gas. Requires highly skilled operator.

Effect on nitrogen form

Treatment process

Organic N NHJNH/ N03'

lon-Exchange

- Ammonium Slight, 80-97% No effect uncertain removal

- Nitrate Slight Slight 75-90

effect effect

Removal Process Process Reference of total advantages disadvantages Chapter nitrogen entering process %

70-95

Can be used where climatic conditions inhibit biological nitrification and where stringent effluent standards are required. Produces a relatively low TDS effluent. Produces a redaimable product (aqueous ammonia). Process may be able to meet total nitrogen standards. Ease of product quality control.

Organic matter in effluent from biological treatment can cause resin binding. Pre-treatment by filtration is usually required to prevent the build up of excessive headloss due to suspended solids accumulation. High concentration of other cations will reduce ammonia removal capability. Regeneration recovery may require the addition of another unit process (e.g., gas stripping). High capital and operating costs. Regeneration products must be disposed of. Requires highly skillled operator.

Effect on nitrogen form

Treatment process

Organic N NHJNHf N03

Membran processes

Electrodialysis

100% of suspended organic N removed

30-50% removed

30-50% removed

Removal Process Process Reference of total advantages disadvantages Chapter nitrogen entering process %

40-50

High degree of nitrogen removal.

Removes all forms of nitrogen.

Chemical precipitaion of salts with low solubility on the membrane surface, dogging of the membrane by the residual colloidal organic matter in waste water effluents usually about 10 per cent of the feed volume, is required to wash the membrane conti-nousty.

Table 1.6 (continued)

Effect on nitrogen form

Treatment process

Organic N NHJNHJ NOj

Removal Process Process Reference of total advantages disadvantages Chapter nitrogen entering process %

Reverse Osmosis

60-90% removed

60-90% removed

60-90% removed

80-90

High amount of nitrogen removed. Removes all forms of nitrogen.

Membrane elements in the reverse osmosis unit can be fouled by colloidal matter. Pre-treatment of a secondary effluent by chemical clarification and some sort of filtration is usually necessary. Iron and manganese in influent can provoke decreased scaling potential. Regular cleaning of membrane necessary.

Precipitation

50-70% removed

Slight effect

Slight effect

20-30

Results in net increase in total dissolved solids of effluent

Large amount of sludge requiring treatment Only organic nitrogen can be easily removed.

Partly adapted from: EPA (1975),

Metcalf and Eddy (1991),

WPCF Nutrient Control Manual (1983),

Weston (1984).

Table 1.7.

The building and running costs of various treatment processes compared with efficiency and reliability of the process. The building and running costs are indicated as expensive, moderate or low.

COST pr

Table 1.7.

The building and running costs of various treatment processes compared with efficiency and reliability of the process. The building and running costs are indicated as expensive, moderate or low.

COST pr

High

Activated sludge Membrane Processes

Rotating Biological Contactors (RBC) Membrane processes

Rotating Biological Contactors (RBC)

Medium

Trickling filters Ion Exchange

Trickling filters Ion Exchange

Activated sludge

Stripping

Precipitation

Low

Submerged filters Trickling filters

Submerged filters

Activated sludge

(Stripping)

(Precipitation)

Low Medium High

NITROGEN CONTENT IN WASTE WATER

Low Medium High

NITROGEN CONTENT IN WASTE WATER

P.E = Personal Equivalent

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