HU204478B - Process for removing phosphorous contene of waste waters with biological strenthening - Google Patents

Abstract

The invention relates to a process for the biologically enhanced removal of the phosphorus of waste waters (effluents), biologically enhanced phosphorus removal being achieved in the purification of domestic, municipal and other industrial waste waters - chiefly containing organic substances. In the process according to the invention, the procedure is carried out in such a manner that the waste water - contacted with activated sludge - is subjected to an anaerobic treatment, then an aerobic and/or anoxic and/or other treatment and, if required, the waste water/activated sludge mixture is allowed to settle. It is characteristic of the process that the sludge concentration of the waste water/activated sludge mixture is established prior to the anaerobic treatment - preferably by sludge recirculation - to a value of 0.01-1.5 kg/m<3>, preferably 0.1-0.5 kg/m<3>, while an aerobic pretreatment having a duration of 1-60 minutes, preferably 5-20 minutes, is carried out on the mixture.

Description

In the process according to the invention, the waste water (1) is subjected to anaerobic, then aerobic and / or anoxic and / or other treatment by contacting the sludge (1) and, if necessary, settling the sludge / sludge mixture. Typically, the process comprises adjusting the sludge concentration of the sewage sludge mixture to 0.01-1.5 kg / m ³ , preferably 0.1-0.5 kg / m ³ , preferably 0.1-0.5 kg / m ³ prior to anaerobic treatment, preferably by sludge recirculation. Aerobic pretreatment is performed for 1-60 minutes, preferably 5-20 minutes.

BACKGROUND OF THE INVENTION The present invention relates to a process for the treatment of wastewater, in which biologically enhanced phosphorus removal is achieved for the purification of municipal, urban and other industrial wastewater, especially containing organic matter. The biological removal of phosphorus is based on creating favorable conditions for the proliferation of polyphosphate-accumulating bacteria, hereinafter referred to as "PAB", in activated sludge. In this way, not only the proportion of phosphorus required for cellular synthesis can be recovered from the effluent, but also the amount of phosphorus accumulated by PAB within the cell in the form of polyphosphate inclusions. The higher the proportion of PAB in activated sludge, the greater the phosphorus removal.

PAB proliferation is facilitated by the introduction of an anaerobic treatment step in front of the usual aerobic or anoxic-aerobic treatment steps. In the anaerobic treatment step, some of the bioavailable components of the incoming wastewater - low molecular weight organic acids - can be utilized and stored by PAB. To do this, they obtain energy from their polyphosphate stores by releasing orthophosphate into their surroundings. In the anaerobic treatment step, other aerobic microorganisms are unable to take up nutrients and are thus disadvantaged. In fact, under aerobic or anoxic conditions, their PAB nutrient stores provide very easy access to the energy and carbon source needed for cellular synthesis, allowing them to multiply faster than others. In an energy-rich aerobic or anoxic environment, they begin to refill their polyphosphate stores. However, in the meantime, not only is the phosphorus released during the anaerobic treatment step reclaimed, but more is recovered, thus removing significant amounts of phosphorus from the wastewater. The built-in phosphorus is then separated from the waste water as excess sludge along with the cell itself.

There are a number of solutions known which aim at solving enhanced biological phosphorus removal by alternating anaerobic and aerobic treatments.

For example, U.S. Pat. A US patent for a activated sludge system to prevent the growth of filamentous biomass and to replace the storage of phosphorus in biomass. During the process, BOD ₅ - (organic matter) and phosphorus-containing wastewater and recirculated sludge are added in an initial anaerobic treatment step. 0 ₂ must be less than 0.7 ppm. This is followed by an aerobic stage followed by sedimentation, from which part of the sludge is recycled for anaerobic treatment. The efficiency of phosphorus removal is the B- ₅ / P content of effluent

and the BOI _S load / sludge concentration.

AT / 35219 publication No. Hungarian invention also discloses the aerobic and anaerobic treatment in the anaerobic stage in which the recirculating slurry is ^upwards: thickened with a stream of higher concentration and thereby higher activity waste water is treated. During the process, aeration is occasionally interrupted in the aerobic step, thereby facilitating the onset of denitrification.

In the present invention, the wastewater is deposited after anaerobic, aerobic and semianaerobic treatment steps. The anaerobic digestion is effected by a maximum of max. They are done during your 2.5-hour stay. The slurry thus fermented is fed to an aerobic pool where the dissolved O0 content exceeds 2 mg / l

DE 3 427 310 and 4721569. The US patent utilizes aerobic-anaerobic and anaerobic-aerobic alternative treatments, which result in increased phosphorus removal with balanced COD removal.

The literature also discloses a number of variants which also aim at improving phosphorus removal. Examples include A / O, A ₂ 0, Bardenpho, Phoredox, UCT, Phostrip, etc. (Hong, S., Krichten, D., Best A., Rachwal, A .: Biological Phosphorus and Nitrogen Removal via the A / O Process, Recent Experience in the United States and United Kingdom) - Wat Sci. Vol 16. No .: 10-11. 1984 -. Further, Arvin, E .: Biological Phosphorus Removal / Systems Design and Operation - Vatten, No .: 4. Lund. 1984 - and also an article published in Water Sci. Tech. (1985, Vol. 17, No. 1112, p. 177).

Basic biochemical processes are widely known, although many issues remain open (Comeau, Y., Hall, KJ, Hancock, REW, Oldham, WK: Biological model for enhanced biological phosphorus removal [Wat. 12.1986]).

The degree of biological phosphorus removal is essentially determined by the amount of low molecular weight organic acids available in the anaerobic treatment step. They come from the wastewater on the one hand and are produced by extracellular enzymatic processes in the anaerobic treatment step.

It is generally known facts and experience that in an anaerobic treatment step, the amount of nutrient uptake is proportional to the amount of phosphorus released. In other respects, the amount of nutrient that can be directly absorbed in a given wastewater determines the amount of phosphorus removal available.

Such nutrients contain incoming wastewater, and the more directly absorbable nutrients from an easily degradable nutrient are produced during anaerobic treatment, the greater the removal of phosphorus.

However, under anaerobic conditions, this conversion, from readily degradable to readily absorbable nutrients, is a slow process. 20 to 30 minutes are usually sufficient to absorb nutrients present in wastewater, while it takes several hours to convert readily degradable materials directly.

Methods so far have attempted to achieve this transformation only through natural extracellular processes in the initial anaerobic zone. However, the BOD content of wastewater can be used more effectively to remove phosphorus. This process is much faster than known aerobic treatment methods, but the resulting easily absorbable materials are also indirectly utilized.

It is an object of the present invention to increase the amount of substances that can be directly absorbed by the PAB in the anaerobic treatment step and / or formed to enhance biological phosphorus removal.

The present invention is based on the discovery that the organic matter content of a given wastewater can be more effectively utilized for the biological removal of phosphorus by performing a small amount of sludge concentration aerobic digestion prior to slow anaerobic digestion processes.

The process according to the invention is characterized in that, prior to anaerobic treatment, the sludge concentration of the sewage sludge mixture is adjusted, preferably by sludge recirculation, to 0.01-1.5 kg / m ³ , preferably 0.1-0.5 kg / m ³ while aerobic pretreatment is carried out for 1-60 minutes, preferably 5-20 minutes, in the sewage sludge mixture, and, if necessary, the post-sedimented sludge or part of it is subjected to anaerobic relaxation of 2-16 hours, preferably 4 hours and recirculating while removing phosphorus from the supernatant by adding chemical and / or de-phosphorus from known anaerobic sludge or recirculating it.

The extracellular enzymes present in the process undergo rapid aerobic degradation even at low sludge concentrations, but due to their low sludge concentration, microorganisms take up only a small fraction of the resulting products that are critical for biological phosphorus removal. Pre-treatment generates more directly absorbable material than is used during pre-treatment. This pretreatment is a "fortification" in terms of directly absorbable nutrients, followed by an increase in PAB nutrient supply in the anaerobic treatment step, thereby providing enhanced biological phosphorus removal.

Enzymatic degradation requires special conditions compared to conventional aerobic wastewater treatment processes. If aerobic treatment is carried out at a concentration of sludge such that the amount of enzyme is sufficient to carry out extracellular degradation but is not sufficient to fully absorb the directly absorbable nutrients generated, the wastewater after pretreatment will contain more directly absorbable nutrients than before. Thus, an increased phosphorus release during the pre-treatment, post-aerobic anaerobic treatment step, and consequently, increased accumulation and thereby removal during aerobic treatment.

Aerobic treatment time is significantly shorter than that of anaerobic treatment with a similar purpose and the subsequent anaerobic step is also significantly shorter.

The present invention ensures that activated sludge that undergoes organic matter degradation absorbs as few small molecule products as possible while maximally decomposing with its extracellular enzymes. For the same reasons, the short treatment duration of the treatment should be as short as possible, preferably from a minimum of 1 minute to a maximum of 20 minutes. For materials that are difficult to decompose or at low temperatures for activated sludge organisms, the treatment time can be increased up to 60 minutes. The high suspended solids content of the effluent increases the applied sludge concentration to about 1.5 kg / m ³ , but preferably 0.01-0.5 kg / m ³ higher than the suspended solids content.

During this pre-treatment, the undissolved organic matter in the wastewater is dissolved and thus directly absorbed by the phosphorus-removing micro-organisms. With this nutrient uptake and stored in the anaerobic phase, they then rebuild their aerobic and anoxic degraded polyphosphates and produce extra phosphorus uptake through their growth and growth. This is significantly, about 10-35% higher than that observed for colonies adapted for conventional biological phosphorus removal.

During the anaerobic treatment, therefore increasing the amount of waste orthophosphate content and decrease the dissolved BOD ₅ content. The conditions for anaerobic treatment include not only the lack of oxygen but also the lack of oxidized nitrogen forms (NO ₂ ~, NO ₃ ).

To achieve the latter, an anoxic treatment that also allows denitrification may be included between the anaerobic and aerobic treatment steps. Some of the organic nitrogen forms are also introduced into the process as ammonia. The anaerobic digestion never reaches the methanogenic phase provided by the residence time and acidification of the pH.

Further enhancement of phosphorus removal is preferably achieved by subjecting the sludge from the post-settler, or part thereof, to a longer period of anaerobic rest for 2 to 16 hours prior to recirculation. In this case, the sludge releases some of its stored polyphosphate content into the supernatant, thereby making it more phosphorus-absorbent and also phosphorus-poor. And in the supernatant, phosphorus will be present in a small volume of water at high concentrations, thus facilitating chemical precipitation. Thus, with minimal cost and quantity of chemicals, small amounts

HU 204478 Chemical slurry can remove phosphorus from wastewater.

The technological process of the process according to the invention is illustrated in Figure 1.

The wastewater 1 flows into the pre-aeration space 2, whereby a partial stream 6 / a of sludge recirculation is also introduced. Here, during aerobic pretreatment with a low concentration of sludge, some of the organic matter in the wastewater is dissolved in the solution due to the effect of the extracellular enzymes present, and a minor part is taken up by the activated sludge. The treated wastewater 10 is mixed with a greater 6 / b fraction of the sap recirculation in the anaerobic treatment space 3 and during the anaerobic treatment, most of the organic matter in the solution is absorbed by the phosphorus-removing microorganisms of the activated sludge with degradation of their stored polyphosphate. This section is free of oxygen and oxidized nitrogen. From here, the slurry enters the aerobic treatment space 4, where organic matter is further degraded, and where the phosphorus accumulators take up their phosphorus released in the anaerobic space, and further increase during growth and growth. The treated slurry enters the post-settler 5, from where the purified water 7 flows, a part of the sludge is removed as excess sludge 8, whereby phosphorus removal is also carried out in the system. The other part of the 25 sludge returns to the process as sludge circulation 6 / a, 6 / b. The recirculation sub-stream 6 / a is about 2-8% of the wastewater 1 and the downstream stream 6 / b is 30-150%, depending on the technological conditions, based on the average amount of incoming wastewater 1.

The procedure is illustrated by specific measurements in the following example:

It was run in parallel with A / O (Anoxic-Oxic-System - 1: US Patent No. 4271026) and 35 inventive technologies - Short-Term Low Sludge Concentration Aerobic Pretreatment (LCAP) - Laboratory Model Equipment Typical filtered COD _Cr and orthophosphate phosphorus values were analyzed. Due to the operating conditions, we were able to maintain only a low concentration of sludge: 1.43 kg / m ^{3 for} the A / O system and 1.52 kg / m ³ for the LCAP technology. The sludge was from an unadapted, high-load activated sludge treatment plant. drainage system with 30 minutes anaerobic, 90 minutes aerobic (A / O) and 15 minutes pretreatment, 20 minutes anaerobic, 90 minutes aerobic (LCAP) treatment times. Phosphorus content was artificially increased in the effluent by the addition of phosphate buffer. 50 The filtered COD and orthophosphate phosphorus data were as follows in g / m ³ :

Place run-off A / O szKOI 75.5 41.5 oP-P 21.2 8.1 LCAP szKOI 74.2 41.5 oP-P 21.2 6.8 delete (%): 45 61.8 44.1 67.9

Ratios of scOI / oP-P removed (rate of utilization of filtered COD for phosphorus removal)

2.6 2.27

Note that the difference between oP-P values is greater than adapted sludge and can reach 35%.

It is also apparent from the example shown that more phosphorus can be bioavailable in the wastewater provided by the process of the invention than by the conventional process.

In addition to the above, however, one of the advantages of the process is that

- devotes a greater proportion of the organic load of the waste water to phosphorus removal,

existing systems can be converted at low cost to implement the process of the invention

Claims (2)

A process, in particular for biologically enhanced removal of phosphorus in organic wastewater containing organic matter, comprising contacting the effluent with anaerobic, then aerobic and / or anoxic and / or other treatment and, if necessary, re-settling the effluent and sludge mixture. that, prior to anaerobic treatment, the sludge concentration of the sewage sludge mixture is preferably adjusted by sludge recirculation to 0.01-1.5 kg / m ³ , preferably 0.1-0.5 kg / m ³ , while the sludge sludge mixture is 1 Aerobic pretreatment is carried out for -60 minutes, preferably 5-20 minutes, and, if necessary, the post-sedimented sludge or part thereof after a period of 2-16 hours, preferably 4 hours, is recirculated as needed to enhance purification and recirculate while the supernatant and / or an The aerobic sludge or a portion thereof is de-phosphorused by known chemical treatment and recirculated. A process according to claim 1, wherein the pretreatment sludge concentration is adjusted to a concentration greater than 0.01-0.5 kg / m ³ above the suspended solids content of the wastewater.