CS257010B1 - A method of removing ammonia from wastewater, particularly from the chemical treatment of oil and coal - Google Patents

Abstract

The method of removing ammonia from wastewater, originating in particular from the chemical processing of oil and/or coal, consists in that the pre-treated wastewater is introduced into an activation tank, in which denitrification and nitrification zones are formed in series at least twice in succession, the activation mixture is recirculated from each nitrification zone to the preceding denitrification zone, the separated biomass is recirculated to the first pre-denitrification zone, where the activation mixture from the first nitrification zone is further recirculated and wastewater with an easily biologically usable substrate with a BOD5 concentration of 5 to 100 kg.m3 is added, and the pre-treated wastewater is introduced into the nitrification zones, with 5 to 50% of the inflow being fed to the last nitrification zone when nitrification is fully underway, with this proportion of the inflow being controlled according to the permissible concentration of nitrogen oxide forms in the effluent, according to the intensity of internal recirculation from the last nitrification zone to the preceding denitrification, according to the recirculation ratio of the return flow and the ammonia concentration in the influent.

Description

The invention relates to the biological removal of ammonia from waste waters, in particular from the chemical treatment of oil and coal, by a combination of assimilation, nitrification and denitrification processes.

During the chemical processing of oil and coal, waste water with ammonia content exceeding the permitted concentrations for discharge of waste water into the recipient is formed in the processing process components. Ammonia from these waste water is usually removed by distillation processes followed by treatment of the obtained ammonia gas into a liquid product or by using the obtained concentrated ammonia water for the production of agricultural fertilizers or direct fertilization.

This method of removing ammonia from waste water is demanding on the plant, which entails considerable investment costs and, due to the operating cost, is suitable mainly for waste water with a high ammonia content. Here, too, complications can occur, as the obtained product is contaminated with organic substances making it difficult to prevent its further use. A further disadvantage of distillation of ammonia is the relatively high residual 1 2 - 1 concentrations of ammonia in the treated effluent, of the order of 10 to 10 mg.l, unless potassium alkalinization of the distillation mixture is used.

However, the alkalization used requires subsequent neutralization of the waste water prior to further treatment or discharge, which further complicates the situation and increases operating costs, and furthermore adversely increases the salinity of the effluent to the recipient.

The use of ion exchange resins for the removal of ammonia from waste water coming mainly from chemical processing of oil and coal encounters the problems of resistance of ion exchangers to the present organic substances and also the problem of treatment of ammoniacal salt concentrates.

The investment costs of building the necessary equipment usually represent a considerable amount. The application of the process of precipitation of ammonia from waste water to the insoluble magnesium-ammonium phosphate followed by the use of the precipitate as fertilizer is again complicated by the combination of the precipitate with organic, in particular odorous substances, preventing its agricultural use.

So far, published biological processes for the removal of ammonia from waste waters mainly derived from chemical processing of oil and / or coal utilize a combination of assimilation, nitrification and denitrification processes, usually arranged as the first purification stage with conventional activation treatment to remove nitrification threatening substances and the next stage is in different order of the nitrification and denitrification stages, either in the arrangement with one biological sludge or with several separate sludges.

Multi-sludge arrangements make it possible to optimize the conditions in the individual stages, but require separate reaction and settling tanks fitted with pumping technology enabling the recirculation of biological sludge. Furthermore, multi-sludge systems are demanding on the necessary neutralizing chemicals for nitrification and an easily assimilable substrate for denitrification. Single-sludge systems of biological removal of ammonia from waste water have a common settling tank, nitrification and denitrification zones are usually realized by dividing the reaction tank by partitions. The ordering of the zones in the order of denitrification, nitrification with the inflow of wastewater into the denitrification, enables the use of residues of natural wastewater contamination as a substrate for denitrification during the recirculation of the return sludge and the outflow from nitrification to the denitrification.

This process requires high recirculation between the nitrification and denitrification zones to maintain an acceptable nitrate concentration in the effluent from the sewage treatment plant, which increases energy demand and causes high hydraulic loads on the sub-processes. Furthermore, after the usually necessary pre-treatment of waste water coming mainly from chemical processing of oil and coal, the residues of org. the substrate present in the waste water to cover the need for a denitrification process and it is necessary to meter the additional substrate.

Sorting zones In order of nitrification, denitrification followed by brief aeration for

Removal of sodium microbubbles has high demands on the alkalizing agent for the nitrification process and an additional substrate for denitrification is necessary.

In the biological removal of ammonia from waste water coming mainly from chemical processing of oil or coal, after the necessary biological pretreatment, by the so-called Barnard process, it is necessary to feed an additional substrate into the so-called predenitrification zone. At the ammonia concentrations common in these waste waters, it is generally necessary to add the additional substrate to the second, previously so-called endogenous, denitrification zone, to ensure the permissible nitrate concentration at the effluent from the treatment plant. The high recirculation ratio used in the Barnadre process for the so-called internal recycle increases the hydraulic loading of the predenitrification and nitrification zones and increases the energy requirement, and reducing it entails the cost of the necessary alkalinizing agents for the nitrification process.

The aforementioned problems are reduced by a process for the removal of ammonia from waste waters, in particular from 2 chemical oil and / or coal treatments, which according to the invention consists in the fact that biologically pre-treated waste waters with an ammonia content of 0.05 to 0.3 kg.m, usually 0.07 to 0.14 kg.m, are fed into the activation tank, in which they are formed by the oxygen regime and construction alternately in a series of connected denitrification and nitrification zones at least twice in succession, from each nitrification zone the activation mixture is recirculated to the previous denitrification 20 to 300%, preferably 40 to 100% of the feed, the reclaimed biomass from the recovery tank is recirculated with a recirculation ratio of 20 to 200%, preferably 40 to 100% of the feed to the predenitrification zone where the activation mixture is further recirculated from the first nitrification zone and where it flows into the other denitrification zones the current with a high concentration of an easily bioavailable substrate with a BOD concentration of [-5 to

-3 -3 $

100 kg.m, preferably 30 to 60 kg.m, separated in the process of chemical treatment of oil and / or coal, for example a waste water stream from ethanol, methanol, preferably oxoalcohol production and from the biologically pre-treated waste water itself, by removing ammonia by: 5 to 50%, preferably 10 to 30% of the feed is fed to the last nitrification zone, the remainder to the other nitrification zones, wherein the proportion of wastewater inlet to the last nitrification zone is controlled during total nitrification and denitrification , according to the intensity of the internal recirculation in the last two zones, according to the recirculation ratio of the activated flow to feed and the ammonia concentration in the waste water supplied. This proportion can also be expressed by relation. '

Qv C, Q, = 7 ^{(1 + R} k ^{+ r} d>< ^where CT O oo is the ratio of the feed to the last nitrification stage to the total waste water flow, ^c k č

o is the ratio of the concentration of N-NO-j in the last nitrification stage to the concentration of N-NH4 + N-NO2 in the feed,

R ^ is the recirculation ratio from the last nitrification to the previous denitrification zone, R ^ is the return flow recirculation ratio.

Along with the ongoing nitrification and denitrification, organic contamination is assimilated and biological wastewater treatment is also carried out.

Said method of removal of ammonia from waste water originating mainly from chemical treatment of oil and / or coal is advantageous in that the pre-nitrification zone is not hydraulically overloaded by the total wastewater inflow, denitrification takes place at higher biomass concentration and thus higher volumetric intensity. the reaction volume of this zone, or the existing volume, utilize a higher recirculation of the activation mixture from the subsequent nitrification zone for higher removal of nitrogen oxide forms and thereby appropriately adjust the process alkalinity ratio or utilize power reserves to maintain operational reliability while maintaining the recirculation ratio.

Supply of a part of the waste water containing ammonia to the last nitrification zone and regulation of this amount according to the above mentioned rules or relation ^Q to ^C K% ⁼ ί ^{(1 + R} K ^{+ R} D>

It allows the removal of ammonia from waste water, while maintaining the mandatory concentration limits without requiring part of the alkalinizing agents that would need to be used for the proportion of waters fed to the last purification stage, as the alkalinity requirement in the last nitrification stage is covered by excess alkalinity from previous denitrification and nitrification stages.

The process according to the invention is illustrated by the following examples.

Example 1

From pre-treated waste water from chemical processing of oil and coal of pH - 7,8 and COD concentration = 0,250 kg.m ³ , BOD = 0,1 kg.m ³ and N-NH 4 = 0,1 kg.m ³ ammonia was removed on an experimental device by a combined nitrification, denitrification process, in which the following zones were sequentially sequenced: predenitrification nitrification, denitrification and aeration to remove nitrogen microbubbles and assimilate excess substrate from the denitrification zone.

The activation mixture was recirculated from the nitrification to the predenitrification zone, there was also recirculated sludge from the settling tank and the above-mentioned waste water was fed. For lack of organic substrate in sewage was predenitrifikační and denitrifikač_3 into the zone supplied waste water streams from the production of oxoalcohols concentration of BOD ₅ = 30 kg so as to ensure a 1.2 to 1.5-fold excess of BOD with respect to oxygen introduced into the zone in the form of oxidized forms of nitrogen. The total residence time of the wastewater in the plant was 13.2 hours, 3 the average dry sludge concentration of 2.5 kg.m ·, the dissolved concentration

C> 2 in nitrification and aeration zone 2.5 to 3 mg.l \

The recirculation ratio from the nitrification zone to the predenitrification was R = 0.5 and was forced by both the necessary residence time in the predenitrification tank and the capacity of the recirculation transport route. The recirculation ratio of the return sludge was R - 0.42 and was limited by the capacity of the return sludge pump. There were difficulties with the predenitrification zone in this arrangement, because the denitrification process attainable and the residence time in the zone resulted in incomplete nitrate removal and the zone could not be expanded due to the geometry of the tank. The system achieved the following results: BOD outflow _ □ + -3 _3 ·>

0.02 kgm, N-NH. in effluent 0,005 kg.m, N-NO2 in effluent 0,002 kg.m with consumption of hydroxide ⁴ . -1 sodium to maintain the pH in the nitrification of 5.1 to mol.h

Example 2

Ammonia was removed from the same effluent by a system where the following zones were sorted: predenitrification, 1. nitrification, denitrification, and 2. nitrification and waste water were fed directly to the nitrification stages at a calculated ratio. The activation mixture was recirculated from the 1st nitrification to the pre-nitrification and from the 2nd nitrification to the denitrification in the ratio R = 0.5. The return flow recirculation was performed at a ratio R = 0.42.

By balancing the system, the allowable wastewater rate to the 2 nd nitrification stage was calculated, which was determined so that the NO 2 concentration at the plant effluent was 45 mg.l, which is 5 mg.l ¹ lower than the legal limits for other streams. By calculation

The obtained value allowed a dose of 19% feed to the 2nd nitrification stage.

All the technological parameters not mentioned here were identical with the previous method of cleaning.

By reducing the hydraulic load of the predenitrification zone by introducing ammonia-containing waste water directly into the nitrification zone, stabilization of the effect of predenitrification and complete removal of nitrates in this zone was achieved without further claims. The new system achieved the same results in removal of organic contamination as the previous system, the nitrate concentration at the outflow was 45 mg.l and the consumption of sodium hydroxide decreased from 5.1 to mol.h ^- ^ to 4.0 to mol.h ie by 21.5 %.

Example 3

Ammonia was removed from the same effluent as described in Example 2 except that the freed-up capacity of the predenitrification zone compared to Example 1 was utilized by increasing the recycle from the 1st nitrification zone to the predenitrification to R = 1. Other technological parameters remained unchanged. In the ammonia removal process, the same results were achieved in the removal of organic and ammoniacal contamination, the nitrate concentration at the outflow remained at 45 mg.l when the consumption of sodium hydroxide to neutralize decreased to 3.14 to mol.h ^A , which 38%.

Claims (1)

SUBJECT OF THE INVENTION A process for removing ammonia from waste water mainly derived from chemical treatment of oil and / or coal, characterized in that the pre-treated waste water with an ammonia content of 0.05 to 0.3 kg.m ³ , usually 0.07 to 0.14 kg.m ³ is fed to the activation tank _? wherein in each of the nitrification zones the activation mixture is recirculated to the intervening denitrification zone in an amount of 20 to 300%, preferably 40 to 100% of the inflow, 20 to 200%, preferably 40 to 100% of the feed to the first predenitrification zone is recirculated from the settling tank, where the activation mixture is further recirculated from the first nitrification zone and, like other denitrification zones, a high concentration effluent stream is readily biologically a usable -3-3 substrate with a BOD concentration. 5 to 100 kg.m, preferably 30 to 60 kg.m, separated in the process of chemical treatment of oil and / or coal and from the biologically pre-treated wastewater, ammonia is removed by introducing the waste water into nitrification zones, with 5 to 50% preferably 10 to 30% of the feed is fed to the last nitrification zone and the feed rate is controlled by the total nitrification and denitrification according to the permissible concentration of oxidized nitrogen forms in the outflow, according to the intensity of internal recirculation from the last nitrification zone flow and the ammonia concentration in the feed.