392
Y. Argaman et al.
The results indicated that raw wastewater containing sulfide ions was toxic to
the nitrifiers. However short-term aeration easily eliminated that effect. The effect
of heterotrophs on the nitrification was examined by running of the continuous
flow experiments. The results showed that a high nitrification rate of up to 50
mg~ +-N L-1h- 1 can be reached.
The selected method for bacteria immobilization was applied for verification
of the feasibility of nitrification interruption for agricultural needs. The results
showed that nitrification rate was successfully recovered after 3 months of
ammonia starvation. Reactor that received small ammonia portions on a weekly
basis demonstrated excellent immediate recovery.
Two additional subjects are currently being studied: selection of the most
appropriate type of nitrification reactor providing effective washout of the
suspended solids and the most cost- effective method of the autotrophic biomass
development.
A pilot-scale system for estimation of the stability and efficiency of the
complete process (nitrogen and BOD removal) has been built.
1 Introduction
The water pollution problem is accented by a scarcity of drinking water sources in
Israel that requires intensive reuse of the general water resources. Such a reuse
creates a danger of accumulation of contaminants in the underground water,
despite their possible low concentrations in the treated wastewater streams. For
example, as result of water pollution by nitrate, a significant part of Israeli
aquifers cannot be used for drinking purposes, because of the serious and
occasionally fatal effects of this compound on infants.
There are many environmental and health problems that can occur due to
presence of the nitrogen compounds in water. The water quality concern with
lakes and reservoirs is eutrofication, a natural aging process in which the surface
water becomes organically enriched. Eutrofication brings a variety of harmful
effects, such as damage to lakes and rivers due to decrease of the transparency or
changes in the color of their water, filter trouble at water purification, and
unpleasant odor or taste of tap water (Metcalf and Eddy 1991). Settling of plant
growth results in sediment oxygen demand, which tends to decrease dissolved
oxygen (DO) levels. Additionally, the presence of ammonium ion can
significantly increase the oxygen demand and cause acidification in the receiving
waters; ammonia (the neutralized form) is toxic to aquatic organisms, especially
fish, even at a concentration as low as 0.5 mg L- 1 (Tramper et al. 1987). Finally,
ammonium ions in waters used for water supply require an increased chlorine
dosage to achieve free chlorine residual in disinfection.
Stringent environmental regulations regarding effluent nitrogen concentration
were established in many countries in the last decade, and growth of the
population requires expansion and modernization of the existing wastewater
treatment plants.
Y. Argaman et al.
The results indicated that raw wastewater containing sulfide ions was toxic to
the nitrifiers. However short-term aeration easily eliminated that effect. The effect
of heterotrophs on the nitrification was examined by running of the continuous
flow experiments. The results showed that a high nitrification rate of up to 50
mg~ +-N L-1h- 1 can be reached.
The selected method for bacteria immobilization was applied for verification
of the feasibility of nitrification interruption for agricultural needs. The results
showed that nitrification rate was successfully recovered after 3 months of
ammonia starvation. Reactor that received small ammonia portions on a weekly
basis demonstrated excellent immediate recovery.
Two additional subjects are currently being studied: selection of the most
appropriate type of nitrification reactor providing effective washout of the
suspended solids and the most cost- effective method of the autotrophic biomass
development.
A pilot-scale system for estimation of the stability and efficiency of the
complete process (nitrogen and BOD removal) has been built.
1 Introduction
The water pollution problem is accented by a scarcity of drinking water sources in
Israel that requires intensive reuse of the general water resources. Such a reuse
creates a danger of accumulation of contaminants in the underground water,
despite their possible low concentrations in the treated wastewater streams. For
example, as result of water pollution by nitrate, a significant part of Israeli
aquifers cannot be used for drinking purposes, because of the serious and
occasionally fatal effects of this compound on infants.
There are many environmental and health problems that can occur due to
presence of the nitrogen compounds in water. The water quality concern with
lakes and reservoirs is eutrofication, a natural aging process in which the surface
water becomes organically enriched. Eutrofication brings a variety of harmful
effects, such as damage to lakes and rivers due to decrease of the transparency or
changes in the color of their water, filter trouble at water purification, and
unpleasant odor or taste of tap water (Metcalf and Eddy 1991). Settling of plant
growth results in sediment oxygen demand, which tends to decrease dissolved
oxygen (DO) levels. Additionally, the presence of ammonium ion can
significantly increase the oxygen demand and cause acidification in the receiving
waters; ammonia (the neutralized form) is toxic to aquatic organisms, especially
fish, even at a concentration as low as 0.5 mg L- 1 (Tramper et al. 1987). Finally,
ammonium ions in waters used for water supply require an increased chlorine
dosage to achieve free chlorine residual in disinfection.
Stringent environmental regulations regarding effluent nitrogen concentration
were established in many countries in the last decade, and growth of the
population requires expansion and modernization of the existing wastewater
treatment plants.