62.What are the methods for measuring cyanide?
Commonly used analysis methods for cyanide are volumetric titration and spectrophotometry. GB7486-87 and GB7487-87 respectively specify the determination methods of total cyanide and cyanide. The volumetric titration method is suitable for the analysis of high-concentration cyanide water samples, with a measurement range of 1 to 100 mg/L; the spectrophotometric method includes the isonicotinic acid-pyrazolone colorimetric method and the arsine-barbituric acid colorimetric method. It is suitable for the analysis of low-concentration cyanide water samples, with a measurement range of 0.004~0.25mg/L.
The principle of volumetric titration is to titrate with standard silver nitrate solution. Cyanide ions and silver nitrate generate soluble silver cyanide complex ions. Excess silver ions react with the silver chloride indicator solution, and the solution changes from yellow to orange-red. The principle of spectrophotometry is that under neutral conditions, cyanide reacts with chloramine T to form cyanogen chloride, which then reacts with apyridine to form glutenedialdehyde, which reacts with apyridinone or barbine Tomic acid produces blue or reddish-purple dye, and the depth of the color is proportional to the cyanide content.
There are some interference factors in both titration and spectrophotometry measurements, and pretreatment measures such as adding specific chemicals and pre-distillation are usually required. When the concentration of interfering substances is not very large, the purpose can be achieved only through pre-distillation.
63. What are the precautions for measuring cyanide?
⑴Cyanide is highly toxic, and arsenic is also toxic. Extra caution must be exercised during analysis operations, and must be performed in a fume hood to avoid contamination of the skin and eyes. When the concentration of interfering substances in the water sample is not very large, simple cyanide is converted into hydrogen cyanide and released from the water through pre-distillation under acidic conditions, and then it is collected through sodium hydroxide washing solution, and then the simple cyanide is converted into hydrogen cyanide. Distinguish simple cyanide from complex cyanide, increase cyanide concentration and lower detection limit.
⑵ If the concentration of interfering substances in water samples is relatively large, relevant measures should be taken first to eliminate their effects. The presence of oxidants will decompose cyanide. If you suspect that there are oxidants in the water, you can add an appropriate amount of sodium thiosulfate to eliminate its interference. Water samples should be stored in polyethylene bottles and analyzed within 24 hours after collection. If necessary, solid sodium hydroxide or concentrated sodium hydroxide solution should be added to increase the pH value of the water sample to 12~12.5.
⑶ During acidic distillation, sulfide can be evaporated in the form of hydrogen sulfide and absorbed by alkali liquid, so it must be removed in advance. There are two ways to remove sulfur. One is to add an oxidant that cannot oxidize CN- (such as potassium permanganate) under acidic conditions to oxidize S2- and then distill it; the other is to add an appropriate amount of CdCO3 or CbCO3 solid powder to generate metal. The sulfide precipitates, and the precipitate is filtered and then distilled.
⑷During acidic distillation, oily substances can also be evaporated. At this time, you can use (1+9) acetic acid to adjust the pH value of the water sample to 6~7, and then quickly add 20% of the water sample volume to hexane or chloroform. Extract (not multiple times), then immediately use sodium hydroxide solution to raise the pH value of the water sample to 12~12.5 and then distill.
⑸ During acidic distillation of water samples containing high concentrations of carbonates, carbon dioxide will be released and collected by the sodium hydroxide washing solution, affecting the measurement results. When encountering high-concentration carbonate sewage, calcium hydroxide can be used instead of sodium hydroxide to fix the water sample, so that the pH value of the water sample is increased to 12~12.5 and after precipitation, the supernatant is poured into the sample bottle.
⑹ When measuring cyanide using photometry, the pH value of the reaction solution directly affects the absorbance value of the color. Therefore, the alkali concentration of the absorption solution must be strictly controlled and the buffer capacity of the phosphate buffer must be paid attention to. After adding a certain amount of buffer, attention should be paid to determine whether the optimal pH range can be reached. In addition, after the phosphate buffer is prepared, its pH value must be measured with a pH meter to see if it meets the requirements to avoid large deviations due to impure reagents or the presence of crystal water.
⑺The change in the available chlorine content of ammonium chloride T is also a common cause of inaccurate cyanide determination. When there is no color development or the color development is not linear and the sensitivity is low, in addition to the deviation in the pH value of the solution, it is often related to the quality of ammonium chloride T. Therefore, the available chlorine content of ammonium chloride T must be above 11%. If it has been decomposed or has turbid precipitate after preparation, it cannot be reused.
64.What are biophases?
In the aerobic biological treatment process, regardless of the form of the structure and the process, the organic matter in the wastewater is oxidized and decomposed into inorganic matter through the metabolic activities of activated sludge and biofilm microorganisms in the treatment system. Thus the wastewater is purified. The quality of the treated effluent is related to the type, quantity and metabolic activity of the microorganisms that make up the activated sludge and biofilm. The design and daily operation management of wastewater treatment structures are mainly to provide a better living environment condition for activated sludge and biofilm microorganisms so that they can exert their maximum metabolic vitality.
In the process of biological treatment of wastewater, microorganisms are a comprehensive group: activated sludge is composed of a variety of microorganisms, and various microorganisms must interact with each other and inhabit an ecologically balanced environment. Different types of microorganisms have their own growth rules in biological treatment systems. For example, when the concentration of organic matter is high, bacteria that feed on organic matter are dominant and naturally have the largest number of microorganisms. When the number of bacteria is large, protozoa that feed on bacteria will inevitably appear, and then micrometazoa that feed on bacteria and protozoa will appear.
The growth pattern of microorganisms in activated sludge helps to understand the water quality of the wastewater treatment process through microbial microscopy. If a large number of flagellates are found during microscopic examination, it means that the concentration of organic matter in the wastewater is still high and further treatment is needed; when swimming ciliates are found during microscopic examination, it means that the wastewater has been treated to a certain extent; when sessile ciliates are found under microscopic examination, When the number of swimming ciliates is small, it means that there are very few organic matter and free bacteria in the wastewater, and the wastewater is close to stable; when rotifers are found under the microscope, it means that the water quality is relatively stable.
65.What is biographic microscopy? what is the function?
Biophase microscopy can generally only be used to estimate the overall condition of water quality. It is a qualitative test and cannot be used as a control indicator for the quality of effluent from wastewater treatment plants. In order to monitor the changes in microfauna succession, regular counting is also required.
Activated sludge and biofilm are the main components of biological wastewater treatment. The growth, reproduction, metabolic activities of microorganisms in sludge and the succession between microbial species can directly reflect the treatment status. Compared with the determination of organic matter concentration and toxic substances, biophase microscopy is much simpler. You can understand the changes and population growth and decline of protozoa in activated sludge at any time, and thus you can preliminarily judge the degree of purification of sewage or the quality of incoming water. and whether the operating conditions are normal. Therefore, in addition to using physical and chemical means to measure the properties of activated sludge, you can also use a microscope to observe the individual morphology, growth movement and relative quantity of microorganisms to judge the operation of wastewater treatment, so as to detect abnormal situations early and take timely measures. Appropriate countermeasures should be taken to ensure the stable operation of the treatment device and improve the treatment effect.
66. What should we pay attention to when observing organisms under low magnification?
Low-magnification observation is to observe the complete picture of the biological phase. Pay attention to the size of the sludge floc, the tightness of the sludge structure, the proportion of bacterial jelly and filamentous bacteria and the growth status, and record and make necessary descriptions. . Sludge with large sludge flocs has good settling performance and strong resistance to high load impact.
Sludge flocs can be divided into three categories according to their average diameter: sludge flocs with an average diameter >500 μm are called large-grained sludge, <150 μm are small-grained sludge, and those between 150 and 500 μm are medium-grained sludge. .
The properties of sludge flocs refer to the shape, structure, tightness of sludge flocs and the number of filamentous bacteria in the sludge. During microscopic examination, sludge flocs that are approximately round can be called round flocs, and those that are completely different from the round shape are called irregular-shaped flocs.
The network voids in the flocs connected to the suspension outside the flocs are called open structures, and those without open voids are called closed structures. The micelle bacteria in flocs are densely arranged, and those with clear boundaries between the floc edges and the external suspension are called tight flocs, while those with unclear edges are called loose flocs.
Practice has proven that round, closed, and compact flocs are easy to coagulate and concentrate with each other, and have good settling performance. Otherwise, the settling performance is poor.
67. What should we pay attention to when observing organisms under high magnification?
Observing with high magnification, you can further see the structural characteristics of micro-animals. When observing, you should pay attention to the appearance and internal structure of micro-animals, such as whether there are food cells in the body of bell worms, the swing of ciliates, etc. When observing the jelly clumps, attention should be paid to the thickness and color of the jelly, the proportion of new jelly clumps, etc. When observing filamentous bacteria, pay attention to whether there are lipid substances and sulfur particles accumulated in the filamentous bacteria. At the same time, pay attention to the arrangement, shape and movement characteristics of the cells in the filamentous bacteria to initially judge the type of filamentous bacteria (further identification of filamentous bacteria). types require the use of an oil lens and staining of activated sludge samples).
68. How to classify filamentous microorganisms during biological phase observation?
Filamentous microorganisms in activated sludge include filamentous bacteria, filamentous fungi, filamentous algae (cyanobacteria) and other cells that are connected and form filamentous thalli. Among them, filamentous bacteria are the most common. Together with the bacteria in the colloidal group, It constitutes the main component of activated sludge floc. Filamentous bacteria have a strong ability to oxidize and decompose organic matter. However, due to the large specific surface area of filamentous bacteria, when filamentous bacteria in the sludge exceed the bacterial jelly mass and dominate the growth, the filamentous bacteria will move from the floc to the sludge. The external extension will hinder the cohesion between flocs and increase the SV value and SVI value of the sludge. In severe cases, it will cause sludge expansion. Therefore, the number of filamentous bacteria is the most important factor affecting sludge settling performance.
According to the ratio of filamentous bacteria to gelatinous bacteria in activated sludge, filamentous bacteria can be divided into five grades: ①00 – almost no filamentous bacteria in the sludge; ②± grade – there is a small amount of no filamentous bacteria in the sludge. Grade ③+ – There are a medium number of filamentous bacteria in the sludge, and the total amount is less than the bacteria in the jelly mass; Grade ④++ – There are a large number of filamentous bacteria in the sludge, and the total amount is roughly equal to the bacteria in the jelly mass; ⑤++ Grade – The sludge flocs have filamentous bacteria as the skeleton, and the number of bacteria significantly exceeds that of the micelle bacteria.
69. What changes in activated sludge microorganisms should be paid attention to during biological phase observation?
There are many types of microorganisms in the activated sludge of urban sewage treatment plants. It is relatively easy to grasp the status of activated sludge by observing changes in microbial types, shapes, quantities and movement states. However, due to water quality reasons, certain microorganisms may not be observed in the activated sludge of industrial wastewater treatment plants, and there may even be no micro-animals at all. That is, the biological phases of different industrial wastewater treatment plants vary greatly.
⑴Changes in microbial species
The types of microorganisms in sludge will change with water quality and operation stages. During the sludge cultivation stage, as activated sludge gradually forms, the effluent changes from turbid to clear, and the microorganisms in the sludge undergo regular evolution. During normal operation, changes in sludge microbial species also follow certain rules, and changes in operating conditions can be inferred from changes in sludge microbial species. For example, when the sludge structure becomes loose, there will be more swimming ciliates, and when the turbidity of the effluent becomes worse, amoebae and flagellates will appear in large numbers.
⑵Changes in microbial activity status
When water quality changes, the activity state of microorganisms will also change, and even the shape of microorganisms will change with the changes in wastewater. Taking bellworms as an example, the speed of the cilia swinging, the amount of food bubbles accumulated in the body, the size of the telescopic bubbles and other shapes will all change with changes in the growth environment. When the dissolved oxygen in the water is too high or too low, a vacuole will often protrude from the head of the bell worm. When there are too many refractory substances in the incoming water or the temperature is too low, the clockworms will become inactive, and food particles can be accumulated in their bodies, which will eventually lead to the death of the insects from poisoning. When the pH value changes, the cilia on the body of the clockworm stop swinging.
⑶Changes in the number of microorganisms
There are many types of microorganisms in activated sludge, but changes in the number of certain microorganisms can also reflect changes in water quality. For example, filamentous bacteria are very beneficial when present in appropriate amounts during normal operation, but their large presence will lead to a reduction in the number of bacterial jelly masses, sludge expansion, and poor effluent quality. The emergence of flagellates in activated sludge indicates that the sludge begins to grow and reproduce, but an increase in the number of flagellates is often a sign of reduced treatment effectiveness. The appearance of a large number of bellworms is generally a manifestation of the mature growth of activated sludge. At this time, the treatment effect is good, and a very small amount of rotifers can be seen at the same time. If a large number of rotifers appear in activated sludge, it often means that the sludge is aging or over-oxidized, and subsequently the sludge may disintegrate and the effluent quality may deteriorate.
Post time: Dec-08-2023
