Eran Friedler

At-source domestic wastewater quality

Abstract Accurate measurement of flow and quality determinands for single or small numbers of dwellings is difficult due to the intermittent nature of flows at source. In this paper, at-source pollutographs are calculated using an alternative approach based on survey data of domestic appliance usage together with measured flow and loads per use. The wastewater pollutograph is built up from the contributions of various appliances. The individual usage of each appliance has been characterised by its frequency together with discharge, duration and loads. The proposed methodology can be used to derive dry weather flow inputs to water quality models, and to assess the impact of changes in local water use and treatment.

Safe on-Site Reuse of Greywater for Irrigation - A Critical Review of Current Guidelines

Reuse of greywater for landscape irrigation can significantly reduce domestic water consumption. Alongside its benefits, there are potential drawbacks to greywater reuse, raising legitimate concerns about the impact on human and environmental health. In this review, a risk assessment framework is used to assess the adequacy of different regulations to ensure safe and long-lasting, onsite greywater reuse for irrigation. Existing regulations from around the world are assessed along with a standardized evaluation of measures taken to protect public and environmental health. In most cases, human health considerations currently dominate regulatory strategies, while environmental risks are either ignored or underrepresented. A distinction between single and multiple households was found to be a fundamental component of the regulations which often lead to approved utilization of untreated greywater among single households. We concluded that the use of untreated greywater is not recommended, especially in multihousehold systems as it may compromise public health, with single household systems posing more likely risks to the environment. Existing rules to control greywater use should be further revised toward the establishment of a more advanced regulatory system which can avert the salient potential risks associated with greywater reuse, while exploiting the enormous potential of this alternative water resource.

Enhancing nitrification in vertical flow constructed wetland utilizing a passive air pump

Abstract Nitrification of simulated secondary effluent solution using a variant of the vertical flow bed constructed wetland was studied. In this system oxygen required for the nitrification process is supplied by a passive air pump. The passive air pump is based on a fill and draw cycle, where oxygen depleted air is removed from the system while fresh air is introduced. Each volume of effluent drained is displaced by an equal volume of fresh air. Spatial and temporal oxygen distribution in the system as a function of drained effluent volume was investigated. Experimental results of nitrification and the corresponding oxygen consumption show good agreement with theoretical calculations based on physico–chemical considerations. Observations show that while oxygen distribution within the media was found to be non-uniform at the beginning of each cycle, it approached more uniform distribution with time. The latter resulted mainly from diffusion of oxygen in the gaseous phase.

Urban rainwater harvesting systems : research, implementation and future perspectives

While the practice of rainwater harvesting (RWH) can be traced back millennia, the degree of its modern implementation varies greatly across the world, often with systems that do not maximize potential benefits. With a global focus, the pertinent practical, theoretical and social aspects of RWH are reviewed in order to ascertain the state of the art. Avenues for future research are also identified. A major finding is that the degree of RWH systems implementation and the technology selection are strongly influenced by economic constraints and local regulations. Moreover, despite design protocols having been set up in many countries, recommendations are still often organized only with the objective of conserving water without considering other potential benefits associated with the multiple-purpose nature of RWH. It is suggested that future work on RWH addresses three priority challenges. Firstly, more empirical data on system operation is needed to allow improved modelling by taking into account multiple objectives of RWH systems. Secondly, maintenance aspects and how they may impact the quality of collected rainwater should be explored in the future as a way to increase confidence on rainwater use. Finally, research should be devoted to the understanding of how institutional and socio-political support can be best targeted to improve system efficacy and community acceptance.

Factors affecting highway runoff quality

Highway runoff often is a significant non-point pollution source. Though it has been extensively studied there are still open questions regarding the identity and mutual influences of the factors affecting pollutant concentrations in road runoff. This review starts with a description of the main pollutants (heavy metals, refractory organics and suspended matter), then it analyzes interactions existing between them and their fractionation between the particulate and dissolved phases. The third section examines the sources of pollution, being: vehicles which contribute fluid and solid pollutants, roads which contribute suspended solids, and dry and wet atmospheric deposition which is influenced by adjacent land-uses. The last section discusses the importance of the factors affecting road runoff quality, the main of which are traffic, rainfall, local conditions (climate and land use) and highway characteristics. The review reveals that conclusions derived from existing data are often ambiguous and significant knowledge gaps still exist.

Greywater use in Israel and worldwide: standards and prospects.

Water shortage around the world enhanced the search for alternative sources. Greywater (GW) can serve as a solution for water demands especially in arid and semi-arid zones. However, issues considered which include acceptability of GW segregation as a separate water treated stream, allowing its use onsite. Consequently, it is the one of next forthcoming water resources that will be used, primarily in the growing mega-cities. It will be even more rentable when combined with the roof runoff water harvesting and condensing water from air-conditioning systems. Reuse of GW is as well beneficial in the mega-cities subject to the high expenses associated with wastewater and fresh water conveyance in the opposite direction. The main problem associated with GW reuse is the quality of the water and the targeted reuse options. At least two main options can be identified: the public sector that is ready to reuse the GW and the private sector which raises extra issues related to the reuse risks. These risk stems from the on yard use of GW, relatively close to the household location. The main focus of the Israeli guidelines for GW use is on the private and single house. The problem is less rigorous in public facilities, where the amounts are relatively large and the raw GW is relatively diluted. The two main principles adopted for reuse are: (i) greywater can be minimally treated since it differs from the black wastes, and; (ii) no contact exists with the resident around. The aggravated standards are an indication of the sensitivity issues related to the problem.

Domestic WC usage patterns

Abstract Despite contributing 30–40% of the total wastewater flow to building drainage systems, little is currently known concerning the detailed usage patterns of the domestic WC. A diary survey of WC usage was carried out on 135 households in southern England over seven consecutive days. Usage was categorised as urine only, faeces only, combined urine and faeces, and other. The urine mode of use followed the expected bimodal pattern of morning and evening peaks, whilst the the number of faecal related flushes peaked only in the morning with no corresponding evening rise. Weekend patterns were shown to differ from week-day usage, particularly in terms of the timing and magnitude of the morning peak. Females were found to use the WC 17% more often than males, whilst males use it 7% more in faecal related mode. Differences were also established between age groups with elderly people apparently having the highest WC usage. The application of cleaning agents was also shown to follow a distinctive diurnal pattern.

Parameters affecting greywater quality and its safety for reuse.

Reusing greywater (GW) for on-site irrigation is becoming a common practice worldwide. Alongside its benefits, GW reuse might pose health and environmental risks. The current study assesses the risks associated with on-site GW reuse and the main factors affecting them. GW from 34 households in Israel was analyzed for physicochemical parameters, Escherichia coli (as an indicator for rotavirus), Pseudomonas aeruginosa and Staphylococcus aureus. Each participating household filled out a questionnaire about their GW sources, treatment and usages. Quantitative microbial risk assessment (QMRA) was performed based on the measured microbial quality, and on exposure scenarios derived from the questionnaires and literature data. The type of treatment was found to have a significant effect on the quality of the treated GW. The average E. coli counts in GW (which exclude kitchen effluent) treated by professionally-designed system resulted in acceptable risk under all exposure scenarios while the risk from inadequately-treated GW was above the accepted level as set by the WHO. In conclusion, safe GW reuse requires a suitable and well-designed treatment system. A risk-assessment approach should be used to adjust the current regulations/guidelines and to assess the performance of GW treatment and reuse systems.

Comparative LCA of decentralized wastewater treatment alternatives for non-potable urban reuse.

Municipal wastewater (WW) effluent represents a reliable and significant source for reclaimed water, very much needed nowadays. Water reclamation and reuse has become an attractive option for conserving and extending available water sources. The decentralized approach to domestic WW treatment benefits from the advantages of source separation, which makes available simple small-scale systems and on-site reuse, which can be constructed on a short time schedule and occasionally upgraded with new technological developments. In this study we perform a Life Cycle Assessment to compare between the environmental impacts of four alternatives for a hypothetical citys water-wastewater service system. The baseline alternative is the most common, centralized approach for WW treatment, in which WW is conveyed to and treated in a large wastewater treatment plant (WWTP) and is then discharged to a stream. The three alternatives represent different scales of distribution of the WW treatment phase, along with urban irrigation and domestic non-potable water reuse (toilet flushing). The first alternative includes centralized treatment at a WWTP, with part of the reclaimed WW (RWW) supplied back to the urban consumers. The second and third alternatives implement de-centralized greywater (GW) treatment with local reuse, one at cluster level (320 households) and one at building level (40 households). Life cycle impact assessment results show a consistent disadvantage of the prevailing centralized approach under local conditions in Israel, where seawater desalination is the marginal source of water supply. The alternative of source separation and GW reuse at cluster level seems to be the most preferable one, though its environmental performance is only slightly better than GW reuse at building level. Centralized WW treatment with urban reuse of WWTP effluents is not advantageous over decentralized treatment of GW because the supply of RWW back to consumers is very costly in materials and energy. Electricity is a major driver of the impacts in most categories, pertaining mostly to potable water production and supply. Infrastructure was found to have a notable effect on metal depletion, human toxicity and freshwater and marine ecotoxicity. Sensitivity to major model parameters was analyzed. A shift to a larger share of renewable energy sources in the electricity mix results in a dramatic improvement in most impact categories. Switching to a mix of water sources, rather than the marginal source, leads to a significant reduction in most impacts. It is concluded that under the conditions tested, a decentralized approach to urban wastewater management is environmentally preferable to the common centralized system. It is worth exploring such options under different conditions as well, in cases which new urban infrastructure is planned or replacement of old infrastructure is required.

Simulation model of wastewater stabilization reservoirs

Abstract Stabilization reservoirs are hypertrophic aquatic systems functioning under non-steady-state conditions. The use of stabilization reservoirs is especially suitable for warm countries suffering from water shortage, where regulation between wastewater production and effluent utilization is needed. Stabilization reservoirs can significantly improve effluent quality; however, only few models have been developed to date. Today, with growing demand for high quality effluent, better understanding of the processes occurring in the reservoirs is needed. This paper describes the development of a mechanistic simulation model that integrates knowledge from the fields of wastewater treatment and limnology. The model has five quality variables in the waterbody and two in the sediment. It was calibrated and verified on three stabilization reservoirs in Israel and exhibited good agreement with observations. Different design and operation alternatives were studied, and some are discussed in this paper. The prediction ability of the model turns it into a useful research and design tool for studying the influence of various design and operation alternatives on the reservoirs’ efficiency as wastewater treatment units.