Background Recently, it has been indicated that anaerobic co-digestion of waste activated sludge with other waste streams at wastewater treatment plants is a promising strategy for enhancing methane production and materials recovery. The enhanced methane production can be used as a renewable source of energy in wastewater treatment plants. It can also reduce the amount of greenhouse gas emission in landfilling of the waste streams. Results According to the results obtained in this study, anaerobic co-digestion of waste activated sludge with mixed fruit waste and cheese whey improves methane production and the quality of digested sludge in comparison to the anaerobic digestion of waste activated sludge individually. It was indicated that carbon/nitrogen ratio (C/N) in the mixture of waste activated sludge, fruit waste and cheese whey improved considerably, leading to better anaerobic organisms’ activity during digestion. With assessing the activity of protease and cellulase, as the main enzymes hydrolyzing organic matter in anaerobic digestion, it was indicated that co-digestion of waste activated sludge with mixed fruit waste and cheese whey enhances the activity of these enzymes by 22 and 9% respectively. At the end of digestion, the amount of cumulative methane production significantly increased by 31% in the reactor with 85% waste activated sludge and 15% mixed fruit waste and cheese whey, compared to the reactor with 100% waste activated sludge. In addition, chemical oxygen demand (COD) and volatile solid (VS) in digested sludge was improved respectively by 9 and 7% when mixed fruit waste and cheese whey was used. Conclusions This study revealed that mixed fruit waste and cheese whey is potentially applicable to anaerobic digestion of waste activated sludge, as fruit waste and cheese whey have high C/N ratio that enhance low C/N in waste activated sludge and provide a better diet for anaerobic organisms. This is of significant importance because not only could higher amount of renewable energy be generated from the enhanced methane production in wastewater treatment plants, but also capital costs of the companies whose waste streams are being transported to wastewater treatments plants could be reduced considerably. Electronic supplementary material The online version of this article (10.1186/s12896-019-0513-y) contains supplementary material, which is available to authorized users.

Background: Scale formation and corrosion continue to cause mild and serious problems in water dispensing systems. Although there are advanced technologies available today, such problems still persist and can lead to health problems and financial damage. Objectives: To delve into this matter, the present study aimed to determine the water potential in terms of scale formation and corrosion in the water resources of villages in the vicinity Harsin town in Iran. Furthermore, the physical and chemical qualities of the water were also studied. Methods: For this descriptive study, samples were prepared from 19 villages during the 8 months of the study duration. These were analyzed according to standard 1053 of Iran water standard and study institution, also calculated for Langelier, Rayzner, Puckorius and aggressive indices for scale formation and corrosion. Results: Indices were 0.80 on Langelier, 6.68 on Rayzner, 10.92 on aggressiveness, and 6.85 on Puckorius calculations. Mean concentrations of calcium, magnesium, fluoride, and ammonium were respectively 63.8 ± 16.89, 21.1 ± 9.08, 0.3 ± 0.26, and 0 ± 0.01 milligram per liter which are reasonable according to national standards. Conclusions: Findings revealed that all physical and chemical indices, and cations and anions of water samples were within a reasonable range. Other parameters involved in causing hardness were also at standard levels. The water resources of Harsin town were healthy in terms of scale formation and corrosion verification, but they still needed close attention in order to keep them within the current appropriate conditions with possible improvements.

We document mercury distribution in the tissues (kidney, liver, breast feathers and pectoral muscle) of a waterbird, the common coot (Fulica atra) from the Kani Barazan wetlands in north-western Iran. Bird samples were collected between November 2011 and January 2012, and mercury was assayed by using a Varian 220 atomic absorption spectrophotometer. Mean levels of mercury in kidney, liver, breast feathers and pectoral muscle were 0.13, 0.22, 0.20 and 0.09 μg/g, respectively. Mercury concentrations in tissues of F. atra were in the following order: liver > feather > kidney > pectoral muscle. The mercury level was significantly (one-way ANOVA, p < 0.05) different between kidneys, livers, pectoral muscles and feathers in F. atra. Although mercury concentrations were higher for all tissues in female birds compared with males, significant (p < 0.05) differences were observed in muscle only.

Background: Cyanobacteria are the most important group of algae. Many factors are involved in the rapid growth of algae such as phosphorus and nitrogen contents. Objectives: The current study aimed at evaluating the effect different phosphorus concentrations on the growth rate of Cylindrospermopsis raciborskii during the aquatic life. Methods: The experiment was carried out for 12 days at three phosphorus concentrations and one control group in Zehnder 8 and Blue-Green 11 media. The rates of cell division per day (G) and specific growth rate (µ) were separately estimated for each group. Cyanobacterium was tested at three phosphorus concentrations; 150, 300, and 600 µg/L. Results: The current study results showed that increasing phosphorus concentration had a significant effect on the growth of C. raciborskii in some particular days of cultivation. The maximum growth rate (0.9 per day) was observed at 7 g/L phosphorus concentration. Conclusions: Phosphorus was a limiting factor and contributed to the removal of toxins from the alga and its blooming. The maximum growth rate was observed in the group treated on the day 8 of cultivation with phosphorus concentration of 300 µg/L.

Background: Data collection tools used in literature to evaluate the degree to which study objectives are fulfilled should be standard to ensure the accuracy of data. Objectives: The present study was performed to standardize and validate a questionnaire designed for investigating the concepts of a health belief model of the style and pattern of using disposable plastic containers. Methods: A review of literature suggests few questionnaires are available on the style and pattern of using disposable containers. In the first step of the present study, the first draft of the questionnaire was designed and its reliability and concepts were evaluated using expert comments. In the second step, its understandability was evaluated in a pilot study on 30 subjects. In the third and fourth steps, the questionnaire reliability was respectively examined using the test-retest and lot quality assurance sampling (LQAS) through calculating a Cronbach's alpha in STATA. Results:The questionnaire subscales included demographic information (8 items), perceived sensitivity (5 items), perceived severity (7 items), practical guidance (3 items), perceived benefits (9 items), perceived barriers (7 items), perceived self-efficiency (8 items), perceived pleasure (6 items) and interpersonal norms (4 items). The questionnaire was distributed among 20 individuals, and they were asked to examine its understandability. At least 80% of the items were acceptable as per quality assurance standards. After revising the questionnaire as required, it was presented to thirty samples. They were also asked to complete the questionnaire again within 15 days, and the results were evaluated for quality assurance. The items were then modified according to the degree to which the objectives were realized. Thirty participants ultimately completed the questionnaire, and the results were evaluated for quality assurance. Conclusions: In a large body of literature, developing standard assessment tools has been considered the main step toward scientific research; nevertheless, standardizing a questionnaire in a way that it is made sensitive can be time-consuming. The present results confirmed the validity and reliability of the designed questionnaire for evaluating the health belief model of patterns of using disposable plastic containers.