Abstract
Introduction
Mechanism of the treating process
Analyses of the biodegradability of anaerobic wine lees tail liquid
Technological process and equipment for the experiment
Results and discussions
Conclusions
DONG Liangjie1 WANG Chunrong1 LI Taihao1
LIU Boxue2 TONG Shusheng2
1. Jilin Agricultural University Changchun, Jilin Province, 130118. China
2. Liaoning Institute of Energy Resources Yingkou, Liaoning Province, 115000. China
Paper No.9405
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The paper deals with the technological process, conditions and operating results of anaerobic wine lees tail liquid aerobically treated with fiber packing biofilm reactor. The main influencing factors and the optimum technological parameters are revealed. Conclusions are discussed. |
Anaerobic digestion -technology has been employed for many years to treat wine lees waste water in wineries. The advantages of this process include less air pollution and valuable by-products in the form of (1) methane gas as a source of energy and (2) stable sludge as a source of fertilizer and soil conditioner. However, the wine lees waste-water treated by anaerobic digestion (referred to as anaerobic wine lees tail liquid in this paper) still does not accord conform to emission standards. Therefore, it is imperative to further treat this liquid.
It has been proved that in order to achieve high efficiency, a biochemical processing reactor must be able to intercept and capture a maximum of microbes and keep these microbes as active as possible. In the past, the general method for intercepting and capturing microbes was to assemble packing materials (such as cinders, plastic rings, and active carbon) into reactors. The disadvantages of these packings are as follows:
1. Both their specific surface areas and their interstitial volume are not big enough.2. These packings increase the complexity of the reactor structure and decrease the mass transfer efficiency.
3. The biofilm mass on these packings increases as the organic load goes up. If the biofilm is too thick, the packings plug up easily. For this kind of reactor the load threshold and the plug-proof facilities should be fixed.
Unlike the above packings, fiber packing, made of polyvinyl alcohol fiber, nylon or polyester fiber, can overcome these disadvantages. In our study, a fiber packing biofilm reactor was adopted to treat anaerobic wine lees tail liquid.
When fiber silk threads are evenly distributed in liquid, each silk thread can be a microbe carrier. Microbes attach onto fiber silk threads in cubical network and form biofilm. Biofilm plays a major role in biofilm waste water treating reactors. While waste water flows past the biofilm, the organic matters and dissolved oxygen in the waste water are transported into the biofilm through a series of mass transfer processes. Then biochemical reactions will occur along the biofilm. As a result, the organic matters are decomposed by microbes and carbon dioxide. The density and thickness of the biofilm increases with the operation period and organic matters. Therefore, an interface between the aerobic layer and the anaerobic layer within the biofilm can be formed. Within the anaerobic layer, which is close to the fiber packing surface, endogenous respiration of the microbes takes place because no or little organic matter is transported into this layer. As a result, the adhesive force of the biofilm is reduced and some biofilm is shed off. New biofilm grows on these packing surfaces where the aged biofilm has been shed off.
In addition, in order to keep the process aerobic, a mechanically aerated system is introduced in the reactor. Aeration makes the fiber packing continuously flutter in the liquid, which not only increases mass transfer efficiency, but also prevents the packing from adhering together.
The standards of waste water quality for aerobically treating include: (1) BOD/COD>0.3; (2) BOD5:N:P=100:5:1; (3) PH=6-9; (4) temperature should be maintained between 15 and 40°C; (5) suspended solid is less than 500mg/liter; (6) concentrations of Zn 2+, Cu 2+, Al3+ , Cr3+ are less than 500mg/liter, 1mg/liter, 1mg/liter, 10mg/liter respectively.
The experimental waste water (the anaerobic wine lees tail liquid) is sampled from the Dalian Longquan (Dragon Fountain) Winery, Liaoning, China. No ions are found in the waste water and the waste water quality is shown in Table 1.
TABLE 1 Composition of the Anaerobic Wine Lees Tail Liquid
|
Variable |
Units of Measurement |
|
COD |
1587 mg/liter |
|
BOD5 |
450.2 mg/liter |
|
Suspended Solid |
1202.5 mg/liter |
|
Total Nitrogen |
457.93 mg/liter |
|
Ammonia Nitrogen |
65.03 mg/liter |
|
Total Phosphorus |
90.73 mg/liter |
|
PH |
7.25 |
|
Temperature |
39±1°C |
The BOD5 curve of the waste water is similar to a typical BOD5 curve which follows first-order reaction kinetics. Therefore, the first-order reaction Kinetics equation (1) is used to calculate the BOD value of the waste water.
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Y=L (1-10-kt) |
(1) |
Where
L = initial ultimate BOD, mg/liter
Y = the amount of BOD that has been exerted at any time, t, mg/liter
K = reaction coefficient, day
t = time, day
Based on the BOD5 curve, using the method of movement suggested by Aiken Field to fit, this yields:
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K = 0.21875 day-1 |
(2) |
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L = 489.14 mg/liter |
(3) |
Based on the L value and Table 1, this yields:
BOD/COD = 0.31
BOD5:N:P = 5:5:1
The above results show that the waste water can be treated with biochemical aerobic process, but the biodegradability is not good enough. In addition, the carbon and nitrogen in the waste water are approximately equal, which can affect the biodegradability.
The technological process flow diagram and equipment for the experiment are shown in Fig.1.
Fig. 1. Technological flow diagram
1. reactor
2. waste water storing tank
3. measuring pump
4. circulating pump of heat water
5. water thermostat bath
6. air flow meter
7. air flow valves
8. air compressor
9. time controller
The reactor has a double-pipe to circulate heating water and to maintain the biochemical process temperature. Based on the temperature of the waste water, the process temperature is chosen at 37±1°C.
1. Effect of Influent COD content on COD Removal Rate
A test on the relationship between the influent COD content and COD removal rate was carried out and the result is shown in Fig.2.
Fig. 2. Relationship Between Influent COD and COD Removal Rate
When the influent COD content ranges from 1000 to 5000 mg/liter the fluctuating maximum of the COD removal rate is 7.1%. The insignificant effect of influent COD content on COD removal rate is obtained by using the method of single factor variance analysis. It suggests that the microbe breeding rate increases with the increasing influent COD content, and microbes can be captured and attached to the fiber packing. According to the process mechanism, it is deducted that the biodecomposition of the organic matter in the liquid follows first-order reaction Kinetics.
2. Effect of HRT on COD Removal Rate
A single factor experiment was carried out to reveal the relation ship between the hydraulic retention time (HRT) and the COD removal rate. The result is shown in Fig.3.
Fig. 3. Relationship between HRT and COD Removal Rate
When the HRT is less than 0.75 days, the COD removal rate goes up. However, the COD removal rate decreases with increased HRT when the HRT exceeds 0.75 days. By observing the experiment process, the following phenomena were discovered: when the HRT was less than 0.75 days, the effluent was clear and had no suspended flocculi; when the HRT exceeded 0.75 days, the effluent was turbid and some suspended flocculi were found in the effluent. These results suggest that digestible organic matter in the waste water is very little when the waste water is detained a long time in the reactor, and this breaks down the balance relationship between nutrients and microbes. As a result, some biofilm disintegrates and the effluent deteriorates.
3. The Effect of Influent COD Content on Packing Volume Removal Load
The relationship curve in Fig. 4 shows when the influent COD content ranges from 1000 to 5000 mg/liter, the packing volume removal loading ranges from 170 to 640 kgCOD/m 3-day.
The result can be explained as follows:
(1) The specific surface area and the interstitial volume of fiber packing are much larger than other packings, and fiber packing can adhere a maximum of microbes. On the other hand, the microbe adhesion space of other type packings is restricted by their specific surface areas and especially restricted by their interstitial volume. As a result, for other packings the volume removal load is 3- 8.5kgCOD/m3-day and these packings are often plugged during operation. For the fiber packing biofilm reactor, after observing a operation period no phenomenon of fiber packing tangling is found and the fluttering characteristic of fiber packing is kept well; some settled biological sludge is found on the reactor bottom. Generally, under conditions of influent 5000 mgCOD/liter, the settled sludge is removed once after about 15 days of operation. The removed sludge volume is equivalent to 1/8--1/6 of the total reactor volume.Fig. 4. Relationship between the Influent COD and the Volume Removal Load
(2) The fluttering of fiber packing in liquid space improves the mass transfer effect. The fluttering of the fiber packing makes the biofilm take on a loose state, which not only promotes the quick release of metabolic products, but also accelerates the diffusion of organic matter into the biofilm. In addition, the biofilm absorbs organic matter throughout the fluttering space, which increases the opportunity for the biofilm to have contact with organic matter and make microbes absorb more organic matter.
4. Effect of Aeration Flow on COD Removal Rate
A single factor experiment was conducted to reveal the relationship between aeration flow and COD removal rate. The result is shown in Fig.5.
According to Fig.5, when the aeration flow ranges from 0.2 to 0.4 liter/min, the effect of the aeration flow on the COD removal rate is insignificant. Within a range of 0.4 to 0.8 liter/min, the COD removal rate becomes increasingly rapid. The COD removal rate peak is obtained when the aeration flow is 0. 8 liter/min. After exceeding 0.8 liter/min, the COD removal rate decreases sharply with the aeration flow down and with some suspended flocculi found in the effluent.
Fig. 5. Relationship between Aeration Flow and the COD Removal Rate
The curve in Fig.5. shows that the fluctuating maximum for the COD removal rate is 42.4%. It suggests that the aeration flow is one of main factors that affects the biochemical process. Under conditions of a definite total air amount, the COD removal rate increases when the aeration flow goes up. In a definite aeration flow, the fluctuation of the COD removal rate with a varied total air amount is small and the fluctuating maximum is only 6%.
Based on this result, it can be deducted that when the bio-film oxygen demand is satisfied, the mass transfer process can be affected by aeration flow. When the aeration flow is controlled within an optimum range, the network structure of the biofilm is at the best loose state, which improves the mass transfer effect and increases the opportunity of contact with organic matter. When the aeration flow exceeds the upper limit of the optimum range, air bubbles will wash the biofilm acutely and, as a result, the biofilm will be peeled off.
5. Optimum Operation Parameters and Operation Result for the Reactor
The optimum operation parameters for the reactor are shown in Table 2, which was obtained by engaging a series of orthogonal experiments and single factor experiments.
Table 2 Optimum Operation Parameters
|
Aeration Flow (liter/min) |
HRT (day) |
Intaking Frequency |
Aeration Time (hour) |
Aeration Interval (hour) |
Temperature (°C) |
|
0.8 |
0.75 |
3 |
0.5 |
0.5 |
37±1 |
In optimum operation parameters, the experiment result for aerobically treating anaerobic wine lees tail liquid with the fiber packing biofilm reactor is shown in Table 3.
Table 3 Experiment Result
|
Variable |
Units of Measurement |
||
|
Effluent (mg/liter) |
Effluent (mg/liter) |
Removal Rate (%) |
|
|
COD |
1587 |
424 |
73.7 |
|
BOD5 |
50.2 |
54.2 |
88.3 |
|
Suspended Solid |
1202.5 |
120.0 |
90 |
|
Ammonia Nitrogen |
65.03 |
52.68 |
19 |
|
Total Nitrogen |
457.93 |
85.7 |
81.3 |
|
Total Phosphorus |
90.75 |
19.94 |
78 |
|
PH |
7.25 |
8.25 |
|
1. It is practicable to aerobically treat anaerobic wine lees tail liquid with a fiber packing reactor. The contents of COD, BOD5, SS in the effluent are 424 mg/liter, 54.2 mg/liter and 120, 0 mg/liter respectively; the removal rates of COD, BOD5, SS are 73.7%, 88.3% and 90% respectively.2. The advantages offered by the reactor include convenient management, operation without plugging, no washback facilities are required and good restarting properties. The experiment stopped once about 15 days after starting, and normal operating conditions were resumed after four days
3. In this process system, suspended solid and anaerobic wine lees tail liquid can be treated together, and an effluent settling tank and effluent settling tank are not required. Therefore, the technological process is simplified.
References
1. D.Barnes, etc, Surveys in Industrial Waste Water Treatment (1) Pitman Advanced Publishing Program, London Melbourne.
2. Yu Ganzhong, Biological Contact Oxidation Process Treating Waste Water, Zhejiang Science Publisher, China, 1984.
3. Liaoning Institute of Energy Resources, Pilot Studies on Treating Wine Lees with UASB, China, 1987.
4. Liaoning Institute of Energy Resources, Fiber Packing Biofilm Fixed-Bed Technology, China, 1989.
