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The paper summarizes the development in the understanding and practical application of the activated sludge process over the last 50 years. Since its invention, the activated sludge process has been a big challenge to design engineers. Traditionally, the technology was covered by sanitary engineers. However, with the development in the understanding of activated sludge process principles, further progress was not possible without knowledge of reaction kinetics and reactor theory. The shift from BOD removal only to combined removal of organic pollution, nitrogen and phosphorus required a chemical engineering approach with outputs of activated sludge microbiology and microbial ecology. Molecular biology enabled more accurate identification of important activated sludge microorganisms. The development in activated sludge process also required more efficient activated sludge separation and thickening. The paper describes the development from secondary clarifiers to membrane separation. Increasing water stress around the globe has also changed the main wastewater paradigm from wastewater treatment and safe discharge to safe reuse.

This study evaluates the suitability of treated wastewater (TWW: secondary effluent and membrane effluent) for crop irrigation and the resultant impact on crop growth and soil physicochemical characteristics. Carrot seeds (Daucus carota subsp. sativus) were grown on loam soil and irrigated with tap water (Tap), secondary effluent (SE), and membrane effluent (ME) until maturity. Bacteriological analyses showed four log counts of E. coli and thermotolerant coliforms for secondary effluent, making it unsafe for the irrigation of carrots. Tap water and membrane effluent fulfilled the microbial limit for water reuse and were suitable for irrigation. The sodium absorption ratio, Kelly index, and magnesium hazard assessments indicated that all three irrigation water streams were suitable for irrigation. The average mass of carrot fruits for Tap, SE, and ME was 2.14 g, 3.96 g, and 3.03 g, respectively. A similar trend was observed for the dry matter composition: Tap had 15.9%, SE had 18.3%, and ME had 16.6%. The soil pH increased from 7.08 to 7.26, 7.39, and 7.33 for tap water-, secondary effluent-, and membrane effluent-irrigated soils, respectively. Nitrate-nitrogen and potassium levels increased in the TWW-irrigated soil, while that of the tap water-irrigated soil decreased. Sodium levels in the TWW-irrigated soil increased significantly but did not induce soil sodicity. The application of the TWW enhanced the growth of the carrot plants and increased the soil nutrient levels. Hence, using TWW in agricultural irrigation could promote food production and also limit the overdependency on freshwater resources. However, TWW should be disinfected by using UV disinfection and ozonation to reduce the risk of microbial contamination. Such disinfection methods may not lead to the formation of toxic byproducts, and therefore secondary pollution to crops is not anticipated.

Emerging contaminants (ECs) are not monitored nor regulated consistently, but may have negative effects on human health and ecosystem balance. Although pharmaceuticals and personal care products are among the main ECs found in surface and wastewater, their toxicity and fate are currently not sufficiently studied. In this study, we analyzed for the first time a group of 46 ECs in the secondary effluent of the wastewater treatment plants (WWTP) of Prague. Thirty-seven compounds were identified in the discharge to surface water. Three compounds had no toxicology information on Artemia salina: furosemide, hydrochlorothiazide, and tramadol. We performed acute toxicity (LC50) tests and enzyme assays after 24 and 48 h at room temperature and 28 °C for these three compounds. LC50 ranged from 225.01 mg/L for furosemide, the most toxic, up to above 14,000 mg/L for tramadol. Changes in enzymatic activity for GST, GPx, AChE, and LDH when A. salina were exposed to LC25 for each contaminant were conspicuous and significant in a contaminant-, exposure time-, and temperature-dependent manner. These biochemical markers complement the toxicity profile of these contaminants in aquatic ecosystems and highlight the need for further research on other ECs and their implications, and the regulations required to protect human and ecological health.

The Conferences on the Design, Operation and Economics of Large Wastewater Treatment Plants (LWWTP) are the most traditional specialized conferences organized by IWA specialist groups. The first conference (at that time called ‘workshop’) was held in Vienna in 1971 and then consecutively every four years in Vienna, until 1987 when the conference began to be held in Budapest (1987, 1999, 2011) and Prague (1991, 2003, 2015) as well. The LWWTP Conference has always been a good place for meeting with leading experts in the field from Europe, USA and Canada, Australia, South Africa, Latin America, South-East Asia and from many other parts of the world. The 2020 conference was planned to be held in Vienna, to celebrate the 50 year anniversary of this great event.

Discharges from wastewater treatment plants have been cited as one of the point sources contributing to surface water quality deterioration. However, does high-quality effluent affect water quality, and contribute significantly to nutrient enrichment or the eutrophication of receiving waters? The Vltava River and a wastewater treatment plant in the Czech Republic were used in a case study, to try to answer these questions through water quality indices and source identification. Samples were collected upstream and downstream of the effluent discharge point, and analyzed for temperature, pH, dissolved oxygen, chemical oxygen demand, nitrate, nitrite, ammonium, phosphate and sulfate. No statistically significant difference (P > 0.05) was observed between most of the upstream and downstream samples’ physicochemical characteristics. The water quality, organic pollution and eutrophication indices of the river, upstream of the effluent discharge point were 83.48, 2.05 and 2.67, respectively, but increased to 99.06, 2.87 and 3.74 downstream. Nutrient source identification using principal component analysis suggests that the increase might be due to the effluent discharge. However, the river's comprehensive ecological (quality classification) status was the same upstream as downstream, indicating that the discharged effluent did not cause nutrient enrichment of the river.

The study evaluated the impact of treated wastewater on plant growth through the use of hyperspectral and fluorescence-based techniques coupled with classical biomass analyses, and assessed the potential of reusing treated wastewater for irrigation without fertilizer application. Cherry tomato (Solanum lycopersicum) and cabbage (Brassica oleracea L.) were irrigated with tap water (Tap), secondary effluent (SE), and membrane effluent (ME). Maximum quantum yield of photosystem II (Fv/Fm) of tomato and cabbage was between 0.78 to 0.80 and 0.81 to 0.82, respectively, for all treatments. The performance index (PI) of Tap/SE/ME was 2.73, 2.85, and 2.48 for tomatoes and 4.25, 3.79, and 3.70 for cabbage, respectively. Both Fv/Fm and PI indicated that the treated wastewater did not have a significant adverse effect on the photosynthetic efficiency and plant vitality of the crops. Hyperspectral analysis showed higher chlorophyll and nitrogen content in leaves of recycled water-irrigated crops than tap water-irrigated crops. SE had 10.5% dry matter composition (tomato) and Tap had 10.7% (cabbage). Total leaf count of Tap/SE/ME was 86, 111, and 102 for tomato and 37, 40, and 42 for cabbage, respectively. In this study, the use of treated wastewater did not induce any photosynthetic-related or abiotic stress on the crops; instead, it promoted crop growth.

The aim of this work was to compare three methods to determinate low concentrations of Paracoccus denitrificans encapsulated in polyvinyl alcohol pellets, which is important for evaluation and optimization of pellet production as well as for monitoring of biomass growth. Pellets with different and well-defined biomass concentrations were used for experiments. The following fast and simple methods were tested: 1. dissolution of polyvinyl alcohol in hot water followed by dry weight estimation, 2. dissolution of polyvinyl alcohol in hot water followed by optical density measurement, and 3. and extraction and quantification of proteins. Dry weight estimation proved to be problematic as it was difficult to separate biomass from polymeric carrier. Optical density measurement showed good linearity of dependence of optical density on biomass content, but determined limits of detection and limits of quantification were not within the range necessary for intended application. The only tested method meeting the requirements for sensitivity was determination of protein concentration after protein extraction. [PUBLICATION ABSTRACT]

This work focuses on the removal of ammonia nitrogen pollution from wastewaters in a two-stage laboratory model based on a combination of the nitritation and anammox processes with the biomass immobilized in a polyvinyl alcohol (PVA) matrix. Owing to the immobilization approach inside the PVA pellets, the bacterial activity remained nearly unchanged on an abrupt change in the environmental conditions. The nitritation kinetics were significantly dependent on the dissolved oxygen concentration. The critical dissolved oxygen concentration at which the nitritation process using the immobilized bacterial culture stops is 0.6 mg/L. The volumetric rate of nitrogen removal by the anammox bacteria was 158 mg/(L·d). The technology presented is well-suited for removing high ammonia nitrogen concentrations (≥300 mg/L).

Increasing incidences of activated sludge foaming have been reported in the last decade in Danish plants treating both municipal and industrial wastewaters. In most cases, foaming is caused by the presence of Actinobacteria; branched mycolic acid-containing filaments (the Mycolata) and the unbranched Candidatus'Microthix parvicella'. Surveys from wastewater treatment plants revealed that the Mycolata were the dominant filamentous bacteria in the foam. Gordonia amarae-like organisms and those with the morphology of Skermania piniformis were frequently observed, and they often coexisted. Their identity was confirmed by FISH, using a new permeabilization procedure. It was not possible to identify all abundant Mycolata using existing FISH probes, which suggests the presence of currently undetectable and potentially undescribed populations. Furthermore, some Mycolata failed to give any FISH signal, although substrate uptake experiments with microautoradiography revealed that they were physiologically active. Ecophysiological studies were performed on the Mycolata identified by their morphology or FISH in both foams and mixed liquors. Large differences were seen among the Mycolata in levels of substrate assimilation and substrate uptake abilities in the presence of different electron acceptors. These differences were ascribed mainly to the presence of currently undescribed Mycolata species and/or differences in foam age.

Activated Sludge - 100 Years and Counting covers the current status of all aspects of the activated sludge process and looks forward to its further development in the future. It celebrates 100 years of the Activated Sludge process, from the time that the early developers presented the seminal works that led to its eventual worldwide adoption.  The book assembles contributions from renowned world leaders in activated sludge research, development, technology and application.  The objective of the book is to summarise the knowledge of all aspects of the activated sludge process and to present and discuss anticipated future developments. The book comprises invited papers that were delivered at the conference \"Activated Sludge…100 Years and Counting!\", held in Essen, Germany, June 12th to 14th, 2014. Activated Sludge - 100 Years and Counting is of interest to researchers, engineers, designers, operations specialists, and governmental agencies from a wide range of disciplines associated with all aspects of the activated sludge process.  Authors: David Jenkins, University of California at Berkeley, USA, Jiri Wanner, Institute of Chemical Technology, Prague, Czech Republic.