Upgrading a facultative pond by implanting water hyacinth

Water hyacinth was implanted in one of two existing facultative ponds and both units were operated in parallel under comparable conditions. The ponds were fed with mainly domestic wastewater after pretreatment in anaerobic ponds and operated at a BOD₅-loading of about 48 kg (ha d)⁻¹ and a detention time of 12 days. This paper covers a period of 4 months, from the implantation of the water hyacinths until no further systematic change in the treatment efficiency of the water hyacinth pond was observed. The median effluent concentrations of the facultative pond for SS, COD, TKN and TP were 55, 95, 6.4 and 1.4 mg l⁻¹, respectively. The values for the water hyacinth pond were 12, 26, 2.5 and 0.4 mg l⁻¹, respectively. The average DO effluent concentration of the water hyacinth pond was 1.2 mg l⁻¹, but this still increased slightly as compared to the influent. The study demonstrates that the implantation of water hyacinth is an appropriate option for upgrading facultative ponds. In many cases where more stringent effluent standards are imposed the method may be a suitable alternative to technical treatment processes.     

Study on chlorine disinfection of pond effluent

Chlorine disinfection experiments were conducted to investigate the die-off patterns of the fecal coliforms when present in waste stabilization pond effluents containing from 100 to 400 mg l⁻¹ algae. The fecal coliform inactivation was observed to occur at two rates, i.e. an initial rapid kill followed by a slower kill. The magnitude of inactivation was found to be proportional to the initial chlorine dose and contact time and inversely proportional to the algal concentration. A mathematical model was developed to predict the fecal coliform survival ratio during the chlorination of the pond effluent. When compared with the experimental data, the predicted results had a correlation coefficient of 0.981.     

Disinfection of advanced wastewater treatment effluent by chlorine, chlorine dioxide and ozone: Experiments using seeded poliovirus

Chlorine, chlorine dioxide and ozone were tested as chemical disinfectants against seeded poliovirus and naturally-occurring fecal coliform organisms in wastewater effluent that had received secondary treatment followed by bench scale advanced wastewater treatment (AWT). The AWT sequence consisted of chemical treatment with lime or alum followed by mixed media filtration. The resulting effluent had low suspended solids concentrations but chemical oxygen demand and nitrogen concentrations only slightly lower than those of secondary effluent. Lime treatment produced greater reductions than alum treatment in virus numbers, but not in fecal coliform organisms.

With both chlorine and chlorine dioxide, in order to reduce seeded poliovirus to less than detectable levels, it was necessary to use doses comparable to those required to disinfect secondary effluent. The required contact times of 30–60 min were also comparable. Utilized ozone doses of 2–4 mg l⁻¹ were required to reduce seeded poliovirus to less than detectable levels in AWT effluent. Naturally-occurring fecal coliform organisms were unaffected at these ozone doses, but were inactivated at higher doses. Because they were more resistant than seeded poliovirus to ozone, fecal coliform organisms show promise as indicators for ozone disinfection.     

Hazards associated with the use of chlorinated oxidation pond effluents for irrigation

Eight milligrams per litre chlorine applied to oxidation pond effluents caused no algal kill within the first 2 h of contact. The available chlorine attacks bacteria causing coliform count to drop from 10⁵ 100 ml⁻¹ to a few tens. Enterovirus counts dropped from about 80 100 ml⁻¹ before chlorination to 37 100 ml⁻¹ (after chlorination). Vibrio cholerae (El-Tor) were killed under these adverse conditions, and MPN dropped from 10³ 100 ml⁻¹ in the influent wastes to 2 100 ml⁻¹ in the effluents. A 5 mg l⁻¹ dose of chlorine at 1 h contact time killed these sensitive bacteria decreasing MPN to less than 2 100 ml⁻¹.Differences between the efficiency of chlorination experiments under laboratory and field conditions would necessitate the application of 15 mg l⁻¹ chlorine for 2 h of contact.     

Decolorization of an azo dye by unacclimated activated sludge under anaerobic conditions

Studies on the reductive decolorization of a complex azo dye, Reactive Red 3.1, were made as part of the development of a practical approach to better exploit the metabolic potential of biomass in wastewater treatment. Decolorization was achieved at low and variable rates by mixed microbial cultures under various environmental conditions, including low pH and high salt concentration. It was caused by reductive cleavage of the azo bond to yield two aromatic amines. More reliable and effective decolorization rates, of up to 20–30 mg l⁻¹ h⁻¹, were given by unadapted activated sludge, (6 g l⁻¹) incubated with 400 mg l⁻¹ of Reactive Red 3.1 under anaerobic conditions. Decolorization also occurred best in static conditions.     

Effect of water hardness on the toxicity of cadmium to micro-organisms

A study was made of the effect of water hardness at different concentrations (viz. 0, 80, 120, 160, 240, 320, 400 and 480 mg l⁻¹ as CaCO₃) on the toxicity of cadmium metal (5 mg 1⁻¹) as sulphate to saprophytic and nitrifying bacteria, with respect to the rate constant (K) and ultimate biochemical oxygen demand (L) which were calculated from BOD data (15 days) using the Thomas Graphical Method. Glucose was used as a source of carbon for micro-organisms. It was observed that the toxicity of cadmium to micro-organisms (both saprophytic and nitrifying) decreased with increasing hardness and reached a maximum at 320 mg 1⁻¹ as CaCO₃ for nitrifying and 400 mg l⁻¹ as CaCO₃ for saprophytic bacteria. After these hardness levels, the ultimate BOD (L) and rate constant (K) showed a decrease. Nitrifying bacteria were found to be more sensitive to the metal as well as to its complexation with calcium or with other ions as they retained their normal activity at a lower hardness level as compared to saprophytic bacteria.     

Interstitial inorganic phosphorus concentrations in lakes Mendota and Wingra

Interstitial P levels in Lake Mendota and Lake Wingra were evaluated as a function of season and water column and sediment depth. Interstitial water was obtained by the centrifugation-filtration method. Temporal variations were observed over the entire 15 cm sediment depth interval examined in all four locations evaluated. Interstitial reactive P (IRP) levels in Lake Mendota ranged from 0.014–1.67 mg l⁻¹ at the 5–6 m water column depth and from 1.20–5.75 mg l⁻¹ at the 18–19.5 m depth. IRP levels in Lake Wingra ranged from 0.029–2.15 mg l⁻¹ at 3.5 m and from 0.191–3.96 mg l⁻¹ at 2 m. Variations in interstitial P were attributed to variations in oxidation state of Fe as influenced by oxygen transport and reduction rates.     

Productivity and nitrogen balance in large scale phytoplankton cultures

Biomass production and nitrogen balance was studied in 35,000 gal (133,000 1) phytoplankton cultures comprising the first stage in a tertiary sewage treatment-mariculture system. The diatom Phaeodactylum tricornutum persisted for most of the study. At secondary sewage effluent loadings sufficient to produce residual dissolved inorganic nitrogen concentrations above approximately 5 μg atoms l⁻¹, an N:C ratio (molar) of 0.17 was obtained and algal growth was not nutrient-limited. Biomass levels, and hence pond particulate carbon and nitrogen output, varied in response to solar irradiance and dilution rate, but not temperature. Mean winter and summer yields were approximately 1 and 5 g (83 and 417 mg atoms) C m⁻² d⁻¹ respectively. An inverse relationship existed between algal biomass concentration and dilution rate, such that in the late spring optimal pond yields occurred between 0.55 and 0.65 dilutions d⁻¹. Better than 95% dissolved total nitrogen removal was obtained. Net dissolved organic nitrogen production, that would offset dissolved inorganic nitrogen removal, did not occur. Pond particulate nitrogen output was usually less than dissolved total nitrogen removal. Probable explanations for this include (1) ammonia evolution to the atmosphere at high pond pH, (2) particulate nitrogen sedimentation, and (3) denitrification. Of these, the first is believed to be quantitatively the most significant.     

Effect of bromide ions on genotoxicity of halogenated by-products from chlorination of humic acid in water

Genotoxicity of halogenated by-products obtained by chlorination of humic acid in water was evaluated in the presence of bromide ions (Br⁻). After the halogenated humic acid solution was made to flow through CSP800 cartridge, absorbed substances were eluted with dimethyl sulfoxide or acetone, and subjected to mutagenicity assays and to analysis of trihalomethanes (THMs). Mutagenic activity was measured by Ames tests using S. typhimurium TA100 strain without metabolic activation, and by the frequencies of micronuclei formation using cultured Chinese hamster lung cells (CHL/IU) in vitro. A powerful effect of bromide ions in chlorinated humic acid solutions was observed on the reverse mutation and micronuclei formations. The formations of total THMs and more brominated THMs were also enhanced in the presence of bromide ions. The ratio of [Br⁻/Cl⁻] regulated the composition and concentrations of THMs intensely, and the rate of substitution of Br⁻ was greater than that of chloride ions (Cl⁻). The increments of the mutagenicity and total THMs formed in chlorinated solutions were observed in parallel with the concentration of Br⁻ or Cl⁻. From the observations, it was concluded that the increasing mutagenicity might be caused by the increasing chlorinated and/or brominated by-products.     

Formation of organic chlorine in activated sludge effluents

Bench scale activated sludge reactors with a solids retention time of 9 days were operated at all combinations of two levels of pH, dissolved oxygen (DO) concentration and feed type (pH 6 and 8; DO 1 and 7 mg 1⁻¹; simple and complex feed). Long-term composite samples were collected and adjusted to neutral pH and equal concentrations of alkalinity and ammonia nitrogen. They were then breakpoint chlorinated with NaO³⁶Cl in order to determine how much chlorine was incorporated into the organic matter. The amounts ranged from 0.019 to 0.067 mg atomic chlorine incorporated per mg soluble organic carbon. Analysis of variance revealed that the DO concentration was the only independent variable to have a significant effect upon the amount of chlorine incorporated, with reactors operated at high DO levels generally producing effluent organics which were less susceptible to adding chlorine.     

An automated procedure for the determination of phosphorus

Procedures for the determination of dissolved orthophosphate and total phosphorus in surface fresh waters (e.g. rivers. lakes and reservoirs) and organic wastes (e.g. domestic sewage. creamery effluents and the like) (particulate or dissolved) are described. Total phosphorus compounds are converted to orthophosphate by acid persulphate digestion. The digestion time is 3 h which goes to completion without any supervision. The method allows for a maximum of 36 samples. 2 blanks and 2 standards to be processed simultaneously. There is no pH adjustment required. Interference from silica and iron(III) up to 20 mg l⁻¹ is absent. Detection limits for the automated step involving orthophosphate are 1 μg 1⁻¹. Recovery and effectiveness of proposed procedures are excellent.     

Regrowth of coliforms and fecal coliforms in chlorinated wastewater effluent

Observations made both in the field in chlorinated effluent, and in laboratory experiments show that coliforms and fecal coliforms are capable of regrowth in chlorinated wastewater. Under field conditions regrowth of coliforms in chlorinated effluent held in a storage reservoir for about 3 days appeared inversely correlated to: (1) The residual chlorine in the storage reservoir and (2) The number of coliforms surviving chlorination. In the laboratory experiments regrowth occurred after initial doses as high as 11 ppm total chlorine even when there was no chemical inactivation of the chlorine. Fecal coliforms did not generally show regrowth to the same extent as coliforms. Regrowth occurred even when coliforms were not detectible in 10-ml of samples after chlorination.Since coliforms and fecal coliforms are capable of regrowth in chlorinated sewage effluent and admixtures of it, the sanitary significance of the number of coliforms after storage or in receiving bodies of water is difficult to interpret. Thus standards might be based on the number of coliforms, or fecal coliforms detected in effluents immediately after chlorination. However, this would not be justified if in addition to coliforms, pathogenic bacteria can regrow in chlorinated effluents.     

Anaerobic biological treatment of phenol at 9.5-15 degrees C in an expanded granular sludge bed (EGSB)-based bioreactor

The aims of this study were to demonstrate the (1) feasibility of psychrophilic, or low-temperature, anaerobic digestion (PAD) of phenolic wastewaters at 10–15 °C; (2) economic attractiveness of PAD for the treatment of phenol as measured by daily biogas yields and (3) impact on bioreactor performance of phenol loading rates (PLRs) in excess of those previously documented (1.2 kg phenol m⁻³ d⁻¹). Two expanded granular sludge bed (EGSB)-based bioreactors, R1 and R2, were employed to mineralise a volatile fatty acid-based wastewater. R2 influent wastewater was supplemented with phenol at an initial concentration of 500 mg l⁻¹ (PLR, 1 kg m⁻³ d⁻¹). Reactor performance was measured by chemical oxygen demand (COD) removal efficiency, CH₄ composition of biogas and phenol removal (R2 only). Specific methanogenic activity, biodegradability and toxicity assays were employed to monitor the physiological capacity of reactor biomass samples. The applied PLR was increased to 2 kg m⁻³ d⁻¹ on day 147 and phenol removal by day 415 was 99% efficient, with 4 mg l⁻¹ present in R2 effluent. The operational temperature of R1 (control) and R2 was reduced by stepwise decrements from 15 °C through to a final operating temperature of 9.5 °C. COD removal efficiencies of c. 90% were recorded in both bioreactors at the conclusion of the trial (day 673), when the phenol concentration in R2 effluent was below 30 mg l⁻¹. Daily biogas yields were determined during the final (9.5 °C) operating period, when typical daily R2 CH₄ yields of c. 3.3 l CH₄ g⁻¹ COD_removed d⁻¹ were recorded. The rate of phenol depletion and methanation by R2 biomass by day 673 were 68 mg phenol g VSS⁻¹ d⁻¹ and 12–20 ml CH₄ g VSS⁻¹ d⁻¹, respectively.     

Shell valve movement response of dark false mussel, Mytilopsis leucophaeta, to chlorination

Shell valve movements of fouling mussel, Mytilopsis leucophaeta, have been studied in the presence of chlorine, using a mussel monitor. Data showed increasing shell valve closure with increasing chlorine concentration. Shell opening rates of M. leucophaeta at control experiments (0 mg litre⁻¹ residual chlorine) were about 10 times more than those at 1 mg litre⁻¹ residual chlorine. Continuous dosing of 0.75 mg litre⁻¹ residual chlorine is required before shell movements are critically affected. Since current environmental stipulations do not permit this, a level of 0.5 mg litre⁻¹ has to be used continuously during settlement periods of M. leucophaeta for their control. The results also indicate that M. leucophaeta is more tolerant to chlorine than other mussel species.     

Effect of settling on performance of the upflow anaerobic sludge bed reactors

The effects of settler volume on the start-up and steady-state performance of 41. laboratory upflow sludge bed reactors treating bean blanching waste of 10,000 mg COD l⁻¹ were determined. The rate of start-up, as well as the maximum loading rate, increased with increased settler volume and performance. A loading rate of 30 kg COD m⁻³ day⁻¹ (based on reactor volume alone) and a COD removal of 95% was obtained with a 21. settling flask and a 4 to 1 recirculation rate. Without a settler, the maximum loading rate was 10 kg COD m⁻³ day⁻¹. The sludge was flocculent rather than granular. Sludge profiles and characteristics in the reactors and settlers were determined.     

Effect of surfactants on the determination of fluoride in waters

Eleven surfactants representing pure cationic anionic and nonionic detergents, four commercial detergents, sodium pyrophosphate, sodium tripolyphosphate, a soap and nitrilotriacetic acid were investigated for their effect on the spectrophotometric and specific ion electrode determinations of fluoride in water. Cationic, anionic and nonionic detergents at concentrations up to 50, 400 and 1000 mg l⁻¹, respectively, gave 5% error or less in the determination of fluoride. Sodium tripolyphosphate interfered badly above 1.5 mg l⁻¹, and therefore the interference by formulated detergents containing tripolyphosphate was large. The fluoride ion activity electrode method is the most suitable procedure for the determination of fluoride in polluted waters containing surfactants.     

Formation equation of halogenated organic compounds when water is chlorinated

Various halogenated organic compounds are formed by chlorination of water. In this study, formation of organic compounds halogenated from a reagent humic acid and extract of a leaf mold were examined under various conditions. The following overall formation equation was obtained from empirical data under the practical wide range when free chlorine remained.

[TOX]=k_TOX[TOC][Cl₂]_ot^β.

Here, [TOX] is the concentration of total organic halogen after t h in units of mg chlorine per liter; [TOC] and [Cl₂]_o are concentrations of total organic carbon and dosed chlorine in units of mg per liter; k_TOX is the rate constant and and β are parameters. From the values of k_TOX, and β, the character of organic substances i.e. precursor of halogenated organic compounds, in water can be evaluated. The values k_TOX, and β for humic acid are 0.053, 0.28 and 0.13, and the values for extract of the leaf mold are 0.032, 0.36 and 0.15, respectively. The activation energies are 10 kJ mol⁻¹ and 11 kJ mol⁻¹ for the reactions of humic acid and leaf mold extract, respectively.     

Treatment of raw domestic sewage in an UASB reactor

The treatment of raw domestic sewage at ambient temperatures in an upflow anaerobic sludge blanket (UASB) reactor with a volume of 120 l. and a height of 1.92 m was studied. The sewage had an average BOD₅ of 357 mg l⁻¹ and COD of 627 mg l⁻¹. Approximately 75% of the organic materials were in the suspended fraction. The sewage temperature ranged from 18 to 28°C during the experimental period. The reactor operated continuously for 9 months and assessed self-inoculation and raw domestic sewage purification. The unit was started without inoculum and ran during the entire experimental period with a hydraulic retention time of 4 h. During the experiment, a sludge bed build-up was observed. At the end of the experimental period, the predominance of spherical granular particles up to 6–8 mm in diameter was evident.

After a 4-month operation, it was observed that the inoculation/acclimatization steps had been concluded. Removal efficiencies of BOD₅ = 78%, COD = 74% and TSS = 72% were obtained. A typical gas production factor of 80 l kg⁻¹ COD added was observed and the CH₄ content of the biogas was 69%.     

Trihalomethane occurrence in chlorinated reclaimed water at full-scale wastewater treatment plants in NE Spain

Total trihalomethane (TTHM) concentrations were determined in three chlorinated effluents (i.e. secondary and tertiary) from full-scale wastewater treatment plants (WWTP) in NE Spain over a 2-year monitoring period (May 2003-February 2005). Low TTHM concentrations (2-30 microg L(-1)), according to international standards for drinking water (80-150 microg L(-1)), were obtained in all samples analysed. The effects of (a) ammonia nitrogen and bromide concentrations, (b) UV light exposure, (c) tank storage, and (d) water temperature were evaluated. Two chlorination strategies were adopted: low chlorine dosages (2-5 mg Cl2 L(-1)) and a high-chlorine dosage (16 mg Cl2 L(-1)). The effects of storing chlorinated reclaimed water and of UV light exposure before chlorination were also evaluated. Samples collected over the 2-year monitoring period offered the possibility to assess the numerous variables affecting THM formation. A statistical evaluation of Platja d'Aro WWTP data set shows a low TTHM formation in the presence of high ammonia nitrogen concentration (p<0.05). That result can be attributed to the formation of chloramines by reaction with added chlorine, at doses below breakpoint chlorination. An increase in TTHM concentration in the presence of bromide (0-1 mg L(-1)) was also recorded (p<0.05). In contrast to published reports, TOC had a negative effect on TTHM formation. COD and turbidity had no statistical significance on TTHM formation. As expected, chlorination promoted TTHM formation in the three water reclamation plants monitored. Nevertheless, no statistical difference was observed when chlorinated effluents were kept in storage tanks. Exposure to UV light did not affect either formation or removal of TTHM. The relative production of TTHM during warm and cold seasons was also evaluated. TTHM production decreased with higher temperatures, but that could be attributed to the increase of ammonia nitrogen concentration observed during the warm summer seasons.     

A simple method for concentrating and detecting viruses in wastewater

A simple method has been developed for routine analysis of sewage and sewage effluents for detecting viruses using adsorption at pH 3 on a 0·45 μm 47 mm diameter membrane filter and elution at pH 8. It was tested on viruses added to autoclaved sewage. Homogenizing the sample for 4 min in a Waring blender and clarification by centrifugation at 1800 g and later at 9230 g facilitated easy filtration without any loss of virus. Retention of the eluant for 30 min on the millipore membrane and then elution in situ under suction provided a sterile eluate with 100 per cent recovery of viruses.

Viruses added to fecal suspensions with 600 mg I⁻¹ BOD were completely recovered when the sample pH was adjusted to 3 and its salt concentration increased by adding 1200 mg l⁻¹ of Mg²⁺ as the chloride. This procedure eliminated the need for passing the samples through ion exchange resins for removing membrane coating components. In a 1 yr programme of monitoring of raw sewage from a middle income group community in Nagpur, a maximum of 3150 PFU/1 during monsoon and 11575 PFU/1 during winter was obtained.

High efficiency and reproducibility of the method allowed the use of sample volumes of 40 ml of raw sewage and 320 ml of treated effluent for the detection of viruses.