Anaerobic waste water treatment

Anaerobic waste water treatment will be employed in place of aerobic processes for many types of effluents in the near future. There is an increased understanding of the fundamentals of the process, and inexpensive high-rate treatment systems are being developed. In 1978 a full scale anaerobic upflow reactor was installed in The Netherlands and this system has since found many applications in industries all over the world. An advanced anaerobic fluid bed installation is now under construction at a bakers' yeast factory in Delft, The Netherlands.     

Effect of temperature on anaerobic treatment of black water in UASB-septic tank systems

The effect of northern European seasonal temperature changes and low temperature on the performance of upflow anaerobic sludge blanket (UASB)-septic tanks treating black water was studied. Three UASB-septic tanks were monitored with different operational parameters and at different temperatures. The results indicated the feasibility of the UASB-septic tank for (pre)treatment of black water at low temperatures with respect to removal of suspended solids and dissolved organic material. Inoculum sludge had little effect on COD(ss) removal, though in the start-up phase some poorly adapted inoculum disintegrated and washed out, thus requiring consideration when designing the process. Removal of COD(dis) was at first negative, but improved as the sludge adapted to low temperature. The UASB-septic tank alone did not comply with Finnish or Dutch treatment requirements and should therefore be considered mainly as a pre-treatment method. However, measuring the requirements as mgCOD l(-1) may not always be the best method, as the volume of the effluent discharged is also an important factor in the final amount of COD entering the receiving water bodies.     

Anaerobic digestion of cattle waste at mesophilic and thermophilic temperatures

Methanogenesis was studied using stirred, bench-top fermentors of 3-1 working volume fed on a semi-continuous basis with waste obtained from cattle fed a high grain, finishing diet. Digestion was carried out at 40 and 60°C. CH₄ production was 11.8, 18.3, 61.9 and 84.5% higher in the thermophilic than the mesophilic digestor at the 3, 6, 9 and 12 g volatile solids (VS) l^–1 reactor volume loading rates, respectively. When compared on an energetic basis CH₄ production was 7.4, 18.3, 72.9 and 107.3 kJ day higher in the thermophilic than the mesophilic digestor. CH₄ production decreased more rapidly with each increase in VS loading rate and decrease in retention time (RT) in the mesophilic than the thermophilic digestor. When expressed as l g^–1 VS fed or as kJ kJ^–1 fed, the amount of CH₄ was 49% less at the highest compared to the lowest loading rate in the mesophilic digestor. In the thermophilic digestor the decrease was only 16%. Propionate accumulated in the mesophilic digestor at the two highest loading rates, reaching concentrations of about 50 mM, but were only about 13 mM in the thermophilic digestor. Isobutyrate, isovalerate plus 2-methylbutyrate, and valerate also accumulated at the higher loading rates.     

Start-up of an UASB-septic tank for community on-site treatment of strong domestic sewage

Two community on-site UASB-septic tanks were operated in parallel over a six months period under two different hydraulic retention times (HRT) of 2 days for R1 and 4 days for R2 at mean sewage temperature of 24 degrees C. The sewage was characterised by a high COD(tot) concentration of 1189 mg/L, with a large fraction of COD(sus), viz. 54%. The achieved removal efficiencies in R1 and R2 for COD(tot), COD(sus), BOD5 and TSS were "56%, 87%, 59% and 81%" and "58%, 90%, 60% and 82%" for both systems, respectively. R2 achieved a marginal but significant (p<0.05) better removal efficiencies of those parameters as compared to R1. The COD(col) and COD(dis) removals in R1 and R2 were respectively 31% and 20%, and 34% and 22%. The sludge accumulation was very low suggesting that the desludging frequency will be of several years. Accordingly, the reactor can be adequately designed at 2 days HRT.     

Anaerobic degradation pathway and kinetics of domestic wastewater at low temperatures

The effect of temperatures below 20 °C (20, 15 and 10 °C) on the anaerobic degradation pathway and kinetics of domestic wastewater fractionated at different sizes was studied in a fluidized-bed batch reactor. The overall degradation pathway was characterized by a soluble fraction degrading according to zero-order kinetics and a colloidal fraction (between 0.45 and 4.5 μm) that first disintegrates into a particulate fraction smaller than 0.45 μm before finally degrading. The colloidal degradation processes follow a first-order kinetic. In contrast, suspended solids (bigger than 4.5 μm) degrade to soluble and colloidal fractions according to first-order kinetics. The colloidal fraction originating from suspended solids further degrades into soluble fraction. These soluble fractions have the same degradation kinetics as the original soluble fraction. The suspended solids degradation was highly affected by temperature, whereas the soluble fraction slightly affected and the colloidal fraction was not affected at all. On the other hand, the colloidal non-degradable fraction increased significantly with the decrease in temperature while the suspended solids slowly increased. The soluble non-degradable fraction was little affected by temperatures changes.     

High-rate anaerobic treatment of wastewater at low temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8 degrees C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids-1 day-1, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40 degrees C.     

Anaerobic treatment of sulphate-containing waste streams

Sulphate-containing wastewaters from the paper and board industry, molasses-based fermentation industries and edible oil refineries present difficulties during anaerobic treatment, leading to problems of toxicity, reduction in methane yield, odour and corrosion. The microbiology and biochemistry of dissimilatory sulphate reduction are reviewed in order to illustrate the potential competition between sulphate reducers and other anaerobes involved in the sequential anaerobic mineralisation process. The theoretical considerations which influence the outcome of competition between sulphate reducers and fermentative, syntrophic, homoacetogenic and methanogenic bacteria are discussed. The actual outcome, under the varying influent organic composition and strength and sulfate concentrations which prevail during digestion of industrial wastewaters, may be quite different to that predicted by thermodynamic or kinetic considerations. The factors governing competitive interactions between SRB and other anaerobes involved in methanogenesis is discussed in the context of literature data on sulphate wastewater treatment and with particular reference to laboratory and full-scale digestion of citric acid production wastewater.     

城市污泥添加厨余垃圾厌氧发酵产挥发性脂肪酸的研究

为了考察污泥产酸工业化的可行性和添加食品废弃物对污泥产酸的影响,本实验在实验室的基础上进行扩大研究,考察了不同的底物总固体浓度对产挥发性脂肪酸的影响.结果显示添加厨余垃圾之后挥发性脂肪酸的累积量可达到17.62g/L.综合产挥发性脂肪酸效果、底物降解效果和产率等情况建议在较大规模的生产过程中选择130g/L的底物浓度为...     

Limits to life at low temperatures and at reduced water contents and water activities

Liquid water is generally considered an absolute requisite for functional life; consequently, life is expected to function only over the range of temperatures that permit its existence. These limits, however, do not apply to cell survival. Some cells can survive the closest attainable approach to 0 K, and some can survive the loss of over 99% of their water.Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.Operated by Union Carbide Corporation under contract W-7405-eng-26 with the U.S. Department of Energy.     

Day and night drift-feeding by juvenile salmonids at low water temperatures

Drift-feeding salmonids in boreal streams face temperatures below physical optima for extensive periods of the year. Because juvenile salmonids react to low water temperatures by becoming nocturnal, knowledge about their foraging ability at low light intensities in cold water is needed to accurately estimate energy intake during non-summer conditions. In a laboratory stream channel, we studied temperature effects on the drift-feeding behaviour of juvenile Atlantic salmon, brown trout, and European grayling in simulated daylight and moonlight at temperatures ranging from 2 °C to 11 °C. Prey capture probability was positively related to temperature, but the temperature dependence did not agree with predictions of the Metabolic Theory of Ecology. Furthermore, reaction distance was positively related to temperature for the three species, which may be one of the underlying mechanisms responsible for the temperature effects on prey capture probability. Overall, the three species had similar capture rates at the different temperature and light levels, although there were species differences. European grayling had a slightly higher prey capture probability than brown trout, and brown trout had a shorter reaction distance than Atlantic salmon and European grayling. These results have implications for both energetics-based drift-foraging theory and for studies of winter ecology.     

Anaerobic treatment of winery wastewater using laboratory-scale multi- and single-fed filters at ambient temperatures

A lab-scale investigation was conducted to examine the effectiveness of a multi-fed upflow anaerobic filter process for the methane production from a rice winery effluent at ambient temperatures. The experiment was carried in two identical 3.0-l upflow filters, a single-fed reactor and a multi-fed reactor. The results showed that the multi-fed reactor, operated at the ambient temperatures of 19–27 °C and influent chemical oxygen demand (COD) of 8.34–25.76 g/l, could remove over 82% of COD even at an organic loading rate (OLR) of 37.68 g-COD/l d and a short hydraulic retention time (HRT) of 8 h. This reactor produced biogas with a methane yield of 0.30–0.35 l-CH₄/g-COD_removed. The multi-fed upflow anaerobic filter was proved to be more efficient than the single-fed reactor in terms of COD removal efficiency and stability against hydraulic loading shocks. A linear-regression model with influent COD concentration and HRT terms adequately described the multi-fed upflow anaerobic filter system for the treatment of rice winery wastewater at ambient temperatures.     

Anaerobic treatability of waste water from pulp and paper industries

A black liquor evaporator condensate from a Kraft mill and a waste water from production of corrugating medium were anaerobically treated on a laboratory scale. The composition of the waste waters was determined before and after treatment in fixed bed reactors.

Toxicity studies by the Microtox-method showed that both waste waters were highly toxic and a slight decrease in toxicity was achieved by anaerobic treatment. Despite the toxicity efficient anaerobic treatment was obtained.

Major components of the condensate were methanol, ethanol, acetone, guaiacol, hydrogen sulfide and dimethyl disulfide. Anaerobic treatment reduced the concentration of the major components considerably with one exception. The concentration of hydrogen sulfide was unchanged.

Organic overloading of the fixed bed reactor or a temperature drop resulted in an accumulation of acetone, although methanol and ethanol were degraded.

Major components of the waste water from the production of corrugating medium were: Klason-lignin, acid-soluble lignin, carbohydrates, extractives and ash. When the fixed bed reactor was operated at a volumetric load of 1.6 kg COD/m³.d the following reductions were obtained:

Klason - lignin (solids fraction 84%; soluble and colloidal fraction 76%), acid-soluble lignin (solids fraction 56%; soluble and colloidal fraction 7%), carbohydrates (100%), extractives (71%), total-S (80%), COD (73%) and BOD₇ (78%).

Kinetic studies showed that condensate was more easily degraded anaerobically than corrugating medium waste water.     

Sulfidogenic fluidized-bed treatment of metal-containing wastewater at low and high temperatures

The applicability of a fluidized-bed reactor (FBR)-based sulfate reducing bioprocess was investigated for the treatment of iron-containing (40-90 mg/L) acidic wastewater at low (8 degrees C) and high (65 degrees C) temperatures. The FBRs operated at low and high temperatures were inoculated with cultures of sulfate-reducing bacteria (SRB) originally enriched from arctic and hot mining environments, respectively. Ethanol was supplemented as carbon and electron source for SRB. At 8 degrees C, ethanol oxidation and sulfate reduction rates increased steadily and reached 320 and 265 mg/L.day, respectively, after 1 month of operation. After this point, the rates did not change significantly during 130 days of operation. Despite the complete ethanol oxidation and iron precipitation, the average sulfate reduction efficiency was 35 +/- 4% between days 30 and 130 due to the accumulation of acetate. At 65 degrees C, a rapid startup was observed as 99.9, 46, and 29% ethanol, sulfate, acetate removals, in respective order, were observed after 6 days. The feed pH was decreased gradually from its initial value of 6 to around 3.7 during 100 days of operation. The wastewater pH of 4.3-4.4 was neutralized by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. As in the low temperature FBR, acetate accumulated. Hence, the oxidation of acetate is the rate-limiting step in the sulfidogenic ethanol oxidation by thermophilic and psychrotrophic SRB. The sulfate reduction rate is three times and acetate oxidation rate is four times higher at 65 degrees C than at 8 degrees C.     

Anaerobic treatment of raw domestic sewage at ambient temperatures using a granular bed UASB reactor

Results obtained in a 120 liter 2 m high UASB-reactor with raw domestic sewage and using a granular sugar beet waste cultivated seed sludge, reveal the feasibility of this type of anaerobic treatment for domestic sewage. Under dry weather conditions 65-85% COD reduction can be achieved at temperatures in the range of 8-20 degrees C and at hydraulic loads as high as 2 m(3) . m(-3) . day(-1). In the case of heavy rainfall the COD-reduction drops to 50-70% and occasionally, viz.at very low influent COD, even below 50%. The net methane production amounts to 7.1-7.3 m(3) . PE(-1) . year(-1), and the excess sludge production ranges form 5.0-8.6 kg TS . PE(-1) . year(-1). Regarding the results obtained anaerobic treatment of raw sewage not only looks an attractive proposition for tropic areas but also for moderate climatic areas.     

Properties of ternary phospholipid/dimethyl sulfoxide/water systems at low temperatures

X-ray diffraction, neutron diffraction and differential scanning calorimetry were used to investigate phase transitions in the ternary system phospholipid/dimethyl sulfoxide (DMSO)/water under cooling for three homologous phospholipids: dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC). Below the temperature of ice formation from -40 to -113 degrees C, a new lamellar phase of DPPC and DSPC was found at and above a DMSO molar fraction of X(DMSO) = 0.05. Below X(DMSO) = 0.05 only a single dehydrated Lc-phase exists after ice formation. The new phase has an increased membrane repeat distance and coexists with a dehydrated Lc-phase. DPPC with a DMSO molar fraction of X(DMSO) = 0.07 shows a membrane repeat distance of the new phase of d = 6.61 +/- 0.03 nm. The value of d increases at the increase of X(DMSO). The new phase was not observed in the ternary system with DMPC. No correlation between the new phase and the glass transition of bound water in the intermembrane space was detected. The new phase was detected only in the systems with excess of water. The creation of the new phase demonstrates the specific DMSO interaction with hydrocarbon chains.     

黑水虻幼虫处理餐厨垃圾过程中体内养分组成与消化酶活性变化规律的研究

黑水虻Hermetia illucens作为一种新型资源环境昆虫,其幼虫可以处理餐厨垃圾、畜禽粪便、蔬菜残体等各种有机废弃物。幼虫富含蛋白质和油脂,可以作为水产饲料的蛋白来源。本研究探索黑水虻幼虫处理餐厨垃圾过程中其养分组成与消化酶活性变化之间的关系。通过黑水虻幼虫自由取食餐厨垃圾,每日采集样品用于物质养分和消化酶活性的测定。结果显示：黑水虻幼虫粗蛋白含量呈现先下降后上升的变化规律,而幼虫总糖含量呈现先上升后下降的变化规律,粗脂肪含量维持上升的趋势。幼虫处理餐厨垃圾过程中,体内蛋白酶在初期迅速上升,第6天后逐渐下降,而淀粉酶呈现出先缓慢上升再迅速上升最后下降的变化规律。脂肪酶在黑水虻幼虫处理餐厨垃圾前期保持较高的活性然后缓慢下降。同时,通过相关性分析,黑水虻幼虫粗蛋白含量变化与蛋白酶活性没有相关性,而总糖与粗脂肪含量变化分别与淀粉酶、脂肪酶有相关性。因此,部分消化酶活性变化与黑水虻幼虫养分组成具有一定的联系,本研究结果为工厂化养殖黑水虻提供一定的理论基础。