Hazen Units Research Articles

Advanced oxidation of recalcitrant chromophores in full-scale MBR effluent for non-potable reuse of leachate co-treated municipal wastewater

Wastewater non-potable reuse involves further processing of secondary effluent to a quality level acceptable for reuse and is a promising solution to combating water scarcity. Recalcitrant chromophores in landfill leachate challenge the water quality for non-potable reuse when leachate is co-treated with municipal wastewater. In this study, we first use multivariate statistical analysis to reveal that leachate is an important source (with a Pearson's coefficient of 0.82) of recalcitrant chromophores in the full-scale membrane bioreactor (MBR) effluent. We then evaluate the removal efficacies of chromophores by chlorination, breakpoint chlorination, and the chlorination-UV/chlorine advanced oxidation treatment. Conventional chlorination and breakpoint chlorination only partially remove chromophores, leaving a colour level exceeding the standards for non-potable reuse (>20 Hazen units). We demonstrate that pre-chlorination (with an initial chlorine dosing of 20 mg/L as Cl2) followed by UV radiation (with a UV fluence of 500 mJ/cm2) effectively degraded recalcitrant chromophores (>90%). By quantifying the electron donating capacity (EDC) and radical scavenging capacity (RSC) of the reclaimed water, we demonstrate that pre-chlorination reduces EDC and RSC by up to 64%, increases UV transmittance by 32%, and increases radical yields from UV photolysis of chlorine by 1.7–2.2 times. The findings advance fundamental understanding of the alteration of dissolved coloured substances by (photo)chlorination treatment and provide implications for applying advanced oxidation processes in treating wastewater effluents towards sustainable non-potable reuse.

An overview of water quality within the Colombo Municipal Council area; A retrospective report analysis

Access to safe and quality drinking water is a fundamental requirement and a basic human right. Water quality is determined by its biological, physical, and chemical properties. Colombo Municipal Council (CMC) area consists of the largest population who utilize pipe-borne water supplied by the National Water Supply and Drainage Board (NWS&DB) Sri Lanka. The objective of the study was to assess the water quality of the drinking water under selected parameters within the Colombo Municipal Council area. In this quantitative, retrospective, cross-sectional study, 268 water analysis reports from 1st July to 30th November 2021 were considered with the permission of the Ethics Review Committee of KIU (KIU_ERC_21_194A) and relevant authorities of NWS&DB. Data on selected parameters such as color, turbidity, pH, Total Dissolved Solids (TDS), Free Residual Chlorine (FRC), the total number of coliform bacteria, and the total number of Escheretia-Coli (E-Coli) were extracted. Data analysis was done using SPSS (Version 25). All values were considered based on reference ranges of Sri Lanka Standards (SLS) guidelines. The study indicated that, among nine water schemes and four water reservoirs, the highest contributions for purification were from the Maligakanda water scheme (15.9% n =56) and Maligakanda water reservoir (51.6%, n=139). All the samples were fully treated water and the mean of the color was 4.03 Hazen Units which was within the permissible level, though ( 3.7 % n=10) of samples exceeded the range. The mean value of the turbidity was 0.49 Nephelometric Turbidity Unit (NTU) which was within the permissible level and only one sample had deviated from the maximum permissible level. The mean pH value was 7.33 and except for one, all other samples were within the permissible level. The mean value of the TDS was 24.51mg/L and the majority (95.8 %, n= 257) of FRC values varied between 0.6-0.8mg/L which was within the permissible level, while 3.39% (n=10) of samples had 0 mg/L. All samples were free from coliform and E-Coli. Most of the samples were within the permissible range of color, pH, turbidity, TDS, FRC, and free from Coliform and E-Coli which can be recommended for use.

Characteristics of immobilized dye-decolorizing peroxidase from Bacillus amyloliquefaciens and application to the bioremediation of dyeing effluent

Dyeing effluent is a major source of aquatic pollution, necessitating novel remediation techniques. In this paper, dopamine-modified, chitosan-coated, halloysite nanotube (HNT) porous microspheres, which are biomimetic entities with a 3D nest-like architecture, were used as a matrix to immobilize dye-decolorizing peroxidase from Bacillus amyloliquefaciens (BaDyP). The porous HNT microspheres showed excellent loading capacity for BaDyP—as high as 250.8 mg/g. Compared with free BaDyP, immobilized BaDyP exhibited better stability over a wide range of pHs and temperatures. At 25 ℃, pH 4.5, and with 2, 2′-azinobis (3-ethylbezthiazoline-6-sulfonate) (ABTS) as an oxidation substrate, the Michaelis constant of immobilized BaDyP was 0.70 mM. The reusability of BaDyP is enhanced by immobilization and approximately 57.6% of the initial activity was retained after six recycling batches. Immobilized BaDyP showed great ability to decolorize various dyes and remediate dyeing effluents. It removed 52.77% of the chemical oxygen demand (COD) and provided 93.93% decolorization (Hazen Units; 89.96% in terms of ADMI), accompanied by significant detoxification within a 72-h incubation period. These results demonstrate the feasibility of using immobilized BaDyP on modified HNTs for the bioremediation of dyeing wastewater. The application of HNT-immobilized BaDyP to the continuous treatment of dyeing effluents in fixed bed reactors will be the next focus of research.

Assessment of phytoplankton composition and physicochemical parameters of Omasi rice field, Anambra State, Nigeria

The microalgae and physicochemical parameters of floodwater of Omasi rice field in Anambra State, Nigeria were studied. Samples for the studies were collected at monthly intervals. The microalgae were studied using light microscopy and identified with taxonomic keys, text books and photograph materials from the internet. The physicochemical parameters and coliform content of the floodwater were analysed using the methods described by the American Public Health Association. Simple means of the parameters and percentages of the algal populations were calculated, while Pearson correlation (p ≤ 0.05) was used to check for significance of the relationships between the investigated parameters. A total of 12 algal taxa belonging to Chlorophyta (48.99%), Cyanophyta (32.89%), Euglenophyta (10.07%), and Bacillariophyceae (8.05%) were recorded in decreasing order of abundance. Water temperature ranged from 26-38 °C with mean of 33.3 ± 2.56 °C; colour ranged from 15-175 Hazen units with mean of 86.25 ± 33.19 Hazen units; depth of water ranged from 7-10.5 cm with mean of 9.38 ± 0.8 cm. Ranges of nitrates and phosphates with their respective means were 0.5-1.8 mg/l (0.86±0.31 mg/l) and 0.79-1.96 mg/l (1.18±0.28 mg/l). Omasi rice field supported the growth of diverse algal groups and species; this may be as a result of available nutrients and good climate as can be deduced from the correlation analyses. Omasi rice field is typical of tropical freshwaters and some tropical rice fields that have been studied in terms of microalgal diversities and some physicochemistry

Investigation of cyanobacteria blooms in paper mill wastewaters and assessment of zinc as a control agent

At a paper manufacturing mill (PML) that had been previously part of an integrated pulp (bisulphite) and paper mills industry, cyanobacterial blooms were observed in the mill’s aerated stabilization basin (ASB) ponds at about 3 years after pulping had been discontinued. This study aimed to determine the factors that led to bloom occurrences and potential control strategies applicable to the paper manufacturing mill’s, aerated stabilization basin system that discharges wastewaters into a coastal lake. Following discontinuation of pulping, the colour of the wastewaters reduced to low levels (~ 10 Hazen units or less), while the levels of nutrient remained potentially supportive of cyanobacteria growth with total phosphorus at ~ 0.1 mg/L and total nitrogen at > 2.5 mg/L. Incidences of blooms in the ABS were associated with preceding average monthly rainfalls and wind speeds being less (~ 44% and ~ 7%, respectively) and average direct sunlight hours being greater (~ 9%) than the long-term average values. Zinc was investigated for control of cyanobacteria as this metal is less toxic to aquatic organisms and microflora than copper algaecides. In laboratory culture trials, zinc was found to inhibit growth of M. aeruginosa (strain MIC338) and Pseudanabaena sp. when dosed at ~ 2.5 mg/L. The inhibition of cyanobacteria by zinc was found to vary between ASB pond samples which had different in situ chlorophyll a levels. This study found that the PML wastewaters investigated can be supportive of cyanobacterial growth to bloom levels after discontinuation of pulping processes and that zinc has potential as a cyanobacteria control agent.

Removal of natural organic matter from aqueous solutions using electrocoagulation pulsed current: optimization using response surface methodology.

The use of the pulsed current can be an alternative to decrease the electrode polarization, as well as achieving lower energy consumption. This study investigated the electrocoagulation through pulsed current for the removal of natural organic matter from water. The experiments were carried out using Box-Behnken factorial design with the response surface methodology for the design of experiments, modeling and interpreting of the results. The electrocoagulation cell consisted of an acrylic reactor with 4 L capacity with four electrodes of aluminum, in parallel connection mode. The experimental independent variables studied were: current density (5.5 to 44.5 A m-2), electrodes spacing (2 to 7.6 mm), stirring rate (200 to 1,000 rpm), frequency (500 to 5,000 Hz), humic acid concentration (5 to 20 mg L-1) and NaCl (100 to 300 mg L-1) as supporting electrolyte, evaluating the residual apparent color (RAC) and electric energy consumption (EEC). The pH of the solution increased during the experiments, reaching basic values. The response surface regression procedure was employed to fit the second-order polynomial, and the model fitted well to the obtained values, reaching R2 0.9995 (RAC) and R2 0.9989 (EEC). The lowest RAC was 11.8 Hazen units (96.2% color removal), where the EEC was 0.393 kWh m-3.

Physico-Chemical Characterization of Rain Water Collected from Industrial Areas of Hisar, India

Rain water samples were collected from five locations from Jindal Chowk, Red Square Market, Grain Market, Milgate and Gangwa of Hisar for physico-chemical properties of rain water, during the months of June, July and August 2013. The first four locations were industrial and market layouts while the last one was a rural, non-industrialized community on the outskirt of Hisar. The result of the rainwater samples indicated the average values of colour (6.6, 6.0, 6.2, 6.0 and 5.0 Hazen units); turbidity (0.18, 0.162, 0.161, 0.163 and 0.16 NTU); chloride (14,12.6, 13.3, 12.6 and 10.6 mg/l); total hardness (23.0, 21.3, 22.0, 15.1 and 14.3 mg/l) at Jindal Chowk, Red Square Market, Grain Market, Milgate and Gangwa respectively. The pH values of the rain water from the four industrial locations indicated slightly acidic i.e. pH<6.6 in the month of June 2013. In this study a correlation was established between the industrial sites and rainwater that water became acidic due the gases emitted by industries.

Assessment of Selected Parameters for Industrial Effluents from Some Industrial Sites in Nairobi, Kenya

The discharge of industrial effluents into the environment poses a threat to human health and is of environmental concern to both plants and animals. Over the last several years there has been a great deal of pollution caused by sewerage treatment works and industrial plants discharging effluents into the environment. This has been caused to a large extent by rapid population increase in the cities and towns, which has led to a strain on the plants' capacities. The industrial effluents from selected industries in Nairobi's Industrial area, Kenya were analyzed to determine the physico-chemical properties which were then compared to the guidelines of the National Environment Management Authority (NEMA). The effluents were collected from four different industrial sites namely General Plastics Industries Ltd., Bhachu Industries Ltd., Chloride Industries and Sameer Africa. pH, color, temperature, chemical oxygen demand (COD), total suspended solids (TSS), total dissolved solids (TDS) and oil and grease were analyzed using standard analytical methods. The results in range form for the four sites were as follows: pH 7.4-8.7; colour 26-44 Hazen units; temperature 20.5-27.7℃; COD 22.22-96.30 mg/L; TSS 25.00-26.37 mg/L; TDS 1080.7-1225.3 mg/L; Oil and Grease 5.71-12.52 mg/L. pH, colour, and oil and grease for effluent outside Sameer Industries were above NEMA guideline values for discharge into the environment. General Plastic Industries had colour, total dissolved solids and oil and grease all above NEMA guideline values. Colour, total dissolved solids and chemical oxygen demand outside Bhachu Industries were also higher. At Chloride Industries only colour was above the guideline value. There is therefore need to use appropriate treatment methods to lower these values.

Influence of the apparent molecular size of aquatic humic substances on colour removal by coagulation and filtration

This study aims to verify the influence of the apparent molecular size of aquatic humic substances (AHSs) on the effectiveness of coagulation with aluminium sulphate and ferric chloride. Coagulation-filtration tests using the jar test and bench-scale sand filters were carried out with water samples having a true colour of approximately 100 Hazen units and prepared with AHSs of different molecular sizes. Stability diagrams are presented showing regions of≥90% and≥95% apparent colour removal delineated for each water sample using plots of total metal ion concentration (Al3+ and Fe3+) versus coagulation pH. To achieve the same degree of colour removal, the water samples with smaller apparent molecular sizes and a higher percentage of fulvic acids required higher dosages of both aluminium sulphate and ferric chloride.

Has the composition of fluvial DOC changed? Spatiotemporal patterns in the DOC‐color relationship

Long‐term increases in dissolved organic carbon (DOC) concentration are now a commonly reported phenomenon across the Northern Hemisphere. Hypotheses proposed to explain the observed increases have implications for changes in DOC composition as well as concentration. This study examines the records of color (Hazen units) and DOC from the UK's Harmonised Monitoring Scheme database from 1974 to 2005 and covers 70 rivers over that period in order to assess whether significant changes in composition have occurred. The records were rarely continuous and so in order to assess the controls and the trends over time, the entire data set was examined as one rather than assessing trends at individual sites. The analysis showed that there was a significant trend over time in the composition of the DOC, as measured by the DOC‐color ratio, but that this declined to a minimum from 1974 to 1989 and has since risen but not returned to 1974 levels. These changes are not explained by variation in flow or by changes in DOC concentrations at the individual sampling sites. The DOC‐color comparison shows that all data can be separated between two independent components: a “light” and a “dark” component; however, variations in these components are driven by increases in DOC concentration and cannot explain the trend in the DOC‐color ratio. A change in the DOC‐color ratio that is independent of DOC and flow that reaches a minimum in 1989 could be explained by changes in soil source water chemistry.

Influência das características das substâncias húmicas aquáticas na eficiência da coagulação com o cloreto férrico

The aim of this study was to verify the influence of the apparent molecular size of aquatic humic substances on the effectiveness of coagulation with ferric chloride. Coagulation-filtration tests using jar test and bench-scale sand filters were carried out on samples of water with true color of approximately 100 Hazen units, prepared with aquatic humic substances of different molecular sizes (F1: < 0.45 µm, F2: 100 kDa - 0.45 µm, F3: 30 - 100 kDa and F4': < 30 kDa). For the water samples with lower apparent molecular size fractions, greater dosages of coagulant was needed to remove the color around 5.0 Hanzen units, mainly because these water samples contain higher concentrations of fulvic acids, which exhibited a larger number of negatively-charged groups.

Seasonal Mixing and Genesis of Endogenic Meromixis in Small Lakes in Southeast Norway

The inland region of Southeast Norway contains many lakes with endogenic meromixis. A synoptic study of seasonal mixing was conducted in 27 oligo- and mesotrophic lakes with surface area 0.0013 – 7.4 km2 and water colour 2-146 Hazen units. The scope was to identify properties of morphometric, optical and chemical nature that lead to development of endogenic meromixis. The summer mixing depths were found to depend on lake area and water colour. Small lakes (&amp;lt; 0.3 km2) were incompletely aerated during the spring circulation and had hypolimnetic temperatures near the temperature of maximum density throughout the summer stagnation. Insubstantial autumn mixing is considered the primary reason lakes in this area develop meromixis. Iron and manganese concentrations in anoxic deep waters depend on concentrations in the sediments and on accumulation of dissolved inorganic carbon in the deep waters. Development of endogenic meromixis is favoured by iron concentration in the sediment more than 5% of dry weight and manganese more than 0.5% of dry weight.

Photocatalytic treatment of humic substances in drinking water

Currently drinking water from the Mourne Mountains in Northern Ireland is treated by the traditional process of coagulation and filtration. Semiconductor photocatalysis was investigated as an alternative. Aldrich humic acid solutions (100 mg dm −3, filtered through 0.22 μm Millipore filters) were photolysed in a 0.1% suspension of Degussa P25 titanium dioxide using a mercury lamp. Degradation of humic acid was followed over time by measuring colour in Hazen units, 254/400 nm absorbance, fluorescence (excitation 237 nm; emission 400 nm) and size exclusion high performance chromatography. The extent of complete oxidation was determined by measuring dissolved organic carbon, chemical oxygen demand and carbon dioxide released. It took approximately 12 min to reduce the humic acid concentration by half; however 50% complete mineralization took 60 min. Some of the intermediates of reaction were highly fluorescent. In the absence of oxygen, light or titanium dioxide no significant degradation occurred.

Spatial and temporal aspects in water chemistry of lakes in Darwin Reserve, Northwest Russia

A diversity of lakes is found throughout Darwin Reserve in northwest Russia that ranges from acid-clear and acid-brown lakes (pH 400 Hazen units) with more neutral pH. The variation among lakes reflects watershed character and watershed interaction with atmospheric deposition. Acid lakes had the highest concentrations of sulfate (5-10 mg/l). Principal components analysis separated lakes based on degree of acidification, nitrogen level, water color, and sulfate concentration. For example, nitrogen levels were higher in neutral lakes than in acid lakes, and sulfate concentrations were negatively related to water color. In contrast, phosphorus levels were comparable among lakes suggesting low retention in watersheds. Mineralized iron was dominant in acid lakes and provided a sink for phosphorus, whereas iron was mostly complexed with organics in neutral lakes. Acid-clear lakes displayed little annual and seasonal fluctuation in water chemistry and that was primarily defined by precipitation; whereas neutral lakes showed much annual and seasonal variability in chemistry due to a greater watershed influence on atmospheric deposition. Results suggest that the influence of atmospheric deposition on lake water chemistry is directly related to the degree of coupling between a lake and its watershed.

Spectrophotometric determination of water colour in hazen units

Colour is a useful index of dissolved humic substances in water. The reference method for colour determination is a visual comparison of samples with reference solutions of hexachloroplatinate, the Hazen method. The precision of this method is poor in relation to common drinking water criteria. A spectrophotometric method with better precision that gives results on the same scale as the Hazen method is described in this paper. Filtration is crucial before spectrophotometric measurement. We found no effect of filtration on true colour. The method has been validated through interlaboratory comparisons. Forty laboratories using this method obtained the same mean values as 20 laboratories using visual judgment. The standard deviations of spectrophotometric measurements were half the values of visual determinations.

The evaluation of colour in natural waters

A model describing the objective evaluation of colour from the transmission properties of natural waters was developed and applied to a wide range of Australian waters. These calculated colours show that measurement of filtered water absorbance at 456 nm calibrated against Pt-Co colour standards agrees with the visually perceived colour intensity by comparator methods and the Pt-Co or Hazen scale of measurement within a maximum error range of ±20%. The error is significantly larger when analytical wavelengths below 440 nm are used. The interference to colour measurement caused by scattering of suspended matter was accounted for at the analytical wavelength. The light scatter component was found to be significant when the ratio of turbidity (in nephelometric turbidity units) to colour (in Hazen units) is greater than 0.02. The use of the 456 nm wavelength is proposed for the standardization of colour measurement in natural waters.

Lake acidity and mercury content of fish in Darwin National Reserve, Russia

Darwin National Reserve is a protected natural area on the north-west shore of the Rybinsk Reservoir, 350 km north of Moscow. In June 1989, six lakes in the Reserve and the reservoir were surveyed to assess lake acidity and the mercury content of perch, Perca fluviatilis. Five were seepage lakes with no permanent inlets or outlets and one was a drainage lake with both an inlet and an outlet. The seepage lakes were acidic (mean pH 4·6–4·8) and varied in colour from 20 to 200 Hazen units. The drainage lake and reservoir were alkaline (mean pH 8·0–8·1) and colour spanned a similar range. The mean mercury content of perch dorsal epaxial muscle ranged from 0·5 to 1·1 μg g −1 wet weight in the five acidic lakes and from 0·1 to 0·2 μg g −1 in the alkaline lakes. Fish mercury contentwas negatively correlated with lake pH ( r = −0·93, P = 0·002)if all waters were considered together, and positively correlated with apparent colour ( r = 0·91, P = 0·03) in the seepage lakes.

A probability model for acid rain data

A class of probability models is proposed for making inferences about the regional distribution of lake alkalinity. This class includes the three-parameter lognormal distribution which is frequently used as a regional model for lake chemistry. The adequacy of the lognormal distribution can be assessed by testing the significance of a single parameter in the proposed model. It is shown that the three-parameter lognormal does not fit the majority of data sets from Eastern Canada. Furthermore, the pH-alkalinity relationship developed by Small and Sutton is used to yield a class of probability models representing the derived distributions for pH. It is shown that there is an improved agreement between the pH-alkalinity relationship and the observations when the water colours are less than or equal to 30 Hazen units.

Physical and chemical characteristics of three acidic, oligotrophic lakes and their watersheds in Kejimkujik National Park, Nova Scotia

Southwestern Nova Scotia receives acidic precipitation (average pH 4.5 to 4.6), and there are many waterbodies that are susceptible to acidification. This study characterizes the physical and chemical features of three remote, oligotrophic lakes and their watersheds in this region, in order to provide baseline information against which assessments can be made of changes caused by atmospheric depositions. Two of the lakes are small (<0.5 km2) and on headwater watersheds: Beaverskin Lake has an almost completely forested watershed and is moderately acidic and clear (pH 5.3, 5 Hazen units), while the watershed of Pebbleloggitch Lake is about 2/3 forested and 1/3 covered by a Sphagnum-heath bog, and its water is very acidic and highly colored (pH 4.3, 87 Hazen units). Kejimkujik Lake is much larger, its watershed is mostly forested but also contains some boggy terrain, its water is intermediate in acidity and color (pH 4.9, 65 Hazen units), and because it drains a much larger area of watershed it has relatively large concentrations of Ca, Mg, Na, Cl, and SO4.

Seasonal variations of water chemistry in oligotrophic streams and rivers in Kejimkujik National Park, Nova Scotia

The seasonal patterns of flow and the concentrations of color, Mg, Ca, H+, Na, Cl, organic anions, SO4, and Gran alkalinity are examined for five streams or rivers in Kejimkujik National Park (Lower Mersey River, Atkins Brook, Grafton Brook, Pebbleloggitch Brook, and Beaverskin Brook). These range in organic color and acidity from very darkwater Atkins Brook (average 191 Hazen units, pH 4.2) to clearwater Beaverskin Brook (5 Hazen units, pH 5.5). In general, most dissolved substances are present in a relatively large concentration during the high-flow period of winter-spring (most notably color, Mg, H+, Ca, Na, organic anions, and SO4). In contrast, Gran alkalinity generally occurs in its highest concentration during the lowflow period. These observations suggest that during the high-flow period, substances are “flushed” from the terrestrial watersheds of these rivers and streams.