Comparison of energy production and carbon emissions from varying biogas dispositions from anaerobic co-digestion at a small-scale wastewater treatment plant

Environmental pollution and increasing water scarcity are key features of the urban landscape of India today. The extension of centralised sewerage networks cannot keep up with city growth, and alternative sanitation systems are needed for citywide inclusive sanitation (CWIS). The government of India mandated larger buildings to be equipped with small-scale wastewater treatment plants (SSTP). This resulted in the emergence of a large number of technology and service providers, and in the implementation of thousands of private SSTPs. However, this quick scaling up was not accompanied by the development of appropriate governance arrangements. As a result, a significant proportion of SSTPs underperform and do not meet the effluent standards. Through a systematic analysis of governance arrangements around SSTPs, this contribution analyses the scaling up process of small-scale wastewater management and reuse at building level in India, in particular in the state of Karnataka and the city of Bengaluru. This paper identifies the gaps in this multi-level, polycentric governance framework and investigates which arrangements are needed to enable the performance of SSTPs on the ground and to create the necessary synergies between the relevant governmental agencies, the private sector and civil society. The scaling up of SSTPs in India mainly followed a market governance approach within a governance environment that is traditionally very hierarchical. The authors argue that hybrid governance arrangements, blending hierarchical, market and network governance are needed to foster market regulation and stakeholder coordination, and increase the performance of the sector. They conclude that an efficient governance of SSS requires the creation of dedicated SSS units at state and city level, and the development of an online platform collating all databases, streamlining and supporting processes from establishment to monitoring, and allowing meaningful collaboration between stakeholders. Through the case study of India, this paper contributes to understand the governance arrangements necessary for the successful scaling up of decentralised sanitation systems, and how to fulfil the potential of alternative solutions for sustainable urban water management. It contributes to governance studies by substantiating the concept of hybrid governance approach and proposing concrete measures to make it work for such distributed systems.

Biotechnological wastewater treatment in small-scale wastewater treatment plants

Although extensive efforts have been made to investigate the dynamics of the occurrence and abundance of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs), understanding the acquisition of antibiotic resistance based on the WWTP scale and the potential effects on WWTPs is of relatively less interest. In this study, metagenomic analysis was carried out to investigate whether the WWTP scale could be affected by the prevalence and persistence of ARGs and mobile genetic elements (MGEs). As a result, 152 ARG subtypes were identified in small-scale WWTP samples, while 234 ARG subtypes were identified in large-scale WWTP samples. Among the detectable ARGs, multidrug, MLS (macrolide–lincosamide–streptogramin), sulfonamide, and tetracycline resistance genes had the highest abundance, and large and small WWTPs had similar composition characteristics of ARGs. In MGE analysis, plasmids and integrons were 1.5–2.0-fold more abundant in large-scale WWTPs than in small-scale WWTPs. The profile of bacteria at the phylum level showed that Proteobacteria and Actinobacteria were the most dominant bacteria, representing approximately 70% across large- and small-scale WWTPs. Overall, the results of this study elucidate the different abundances and dissemination of ARGs between large- and small-scale WWTPs, which facilitates the development of next-generation engineered wastewater treatment systems.

Various forms of energy are used during a wastewater treatment process like electrical, manual, fuel, chemical etc. Most of the earlier studies have focused only on electrical energy intensity of large-scale centralized wastewater treatment plants (WWTPs). This paper presents a methodological framework for analysing manual, mechanical, chemical and electrical energy consumption in a small-scaled WWTP. The methodology has been demonstrated on a small-scale WWTP in an institutional area. Total energy intensity of the plant is 1.046 kWh/m3 of wastewater treated. Electrical energy is only about half of the total energy consumption. Manual energy also has a significant share, which means that the small-scale treatment plants offer significant employment opportunities in newly industrializing countries and replaces fossil fuel-based energy with renewable. There is a lack of sufficient data in the literature for comparison, and few studies have reported values that vary significantly due to the difference in scale, scope of the study and the choice of the treatment technologies. Replication of similar studies and generation of data in this area will offer directions for decision on choice of the scale of wastewater treatment process from the considerations of energy and climate change mitigation strategies.

As a leading nutrient emitter, wastewater infrastructure harbors significant technical potentials to reduce the water-polluting emissions of phosphorus and nitrogen into the Elbe river basin. From the viewpoint of the central infrastructure, the effluent threshold value of urban wastewater treatment plants could be lowered further by advanced use of denitrification and membrane filtration, and storm water overflows of wastewater and contaminated rainwater from sewers could be treated in retention soil filters. In addition, small-scale wastewater treatment plants, infiltration and reducing or unsealing impervious surfaces could be used as decentralized elements of wastewater or storm water treatment. It can be shown that if the most advanced measures were applied in all wastewater-relevant areas, up to 60% of the phosphorus and 37% of the nitrogen emissions could be avoided. Alongside central wastewater treatment plants, small-scale treatment plants prove to be the most effective and cost-efficient option. To achieve an ecologically acceptable state of the Elbe, however, it may be necessary to employ more costly measures as well.

Improvement of phosphorus removal by calcium addition in the iron electrocoagulation process

Small-scale wastewater treatment plants as a source of the dissemination of antibiotic resistance genes in the aquatic environment

Revealing microbial community structures in large- and small-scale activated sludge systems by barcoded pyrosequencing of 16S rRNA gene

The Operation and Maintenance of Small Scale Wastewater Treatment Plants

Indicators for sustainability assessment of small-scale wastewater treatment plants in low and lower-middle income countries

Long-term investigation of phosphorus removal by iron electrocoagulation in small-scale wastewater treatment plants.

Renewable natural gas derived from biogas presents a viable pathway for decarbonizing natural gas systems. Wastewater treatment plants equipped with anaerobic digesters often flare or utilize biogas for heat and electricity generation, missing the potential of renewable natural gas. This study investigates the techno-economic feasibility and emission impact of a renewable natural gas system at a small wastewater treatment plant in the Southwestern United States. Due to a lack of existing data on biogas composition and contaminants from plants originating within the United States, samples were tested seasonally for a year, and gas components are reported in this analysis. Using hourly biogas production data, the analysis incorporates costs and renewable fuel credits at 2022 market prices and the cost to remove the biogas contaminants. The results show a 15-year net present value of USD 16.3 million, with a payback period of three years, surpassing the economic performance of combined heat and power systems previously assessed for the same facility. Additionally, renewable natural gas systems achieve a 22% reduction in site emissions compared to combined heat and power systems. These findings highlight renewable natural gas as a profitable and environmentally superior alternative for biogas utilization in small-scale wastewater treatment plants, contingent on access to renewable fuel credits.

Function and biomass production of willow wetlands applied in the polishing phase of sewage treatment in cold climate conditions

The wastewater treatment is an essential practice and is one of the forefront new worldwide challenges. Indeed, the today aims in wastewater management are profoundly changing. The sanitization processes are of course essential, but now some more efforts are required not only to reduce the environmental impact of the effluent regarding the receiving water body, for example, in terms of organic load, but also to provide management practices to allow water recovery, recycle and reuse. This means that treated wastewater are new resources that may be reused according to their final level of quality. New technological facilities are available, some more are expected in the near future, and innovative scaling approaches are strongly encouraged too. Actually, sometimes extensive sewage collection systems are no more cost-effective, thus decentralisation treatment processes considering small-scale wastewater treatment plants may represent a potential solution in both developed and developing countries. Furthermore, this kind of approach will strengthen those areas that are historically affected by drought phenomena or are expected to suffer from water scarcities in the near future as a consequence of climate change.

This study examines the feasibility of the contact aeration method for utilisation in small-scale domestic wastewater treatment facilities in various rural areas of China, where the national government starts to address the water pollution issue. Three pilot facilities using the contact aeration method with different capacities were constructed, operated and monitored in Chongqing city and Jiangsu province. In order to evaluate the feasibility of the constructed facilities, the quality of treated wastewater and the operational cost were monitored. Results obtained from the monitoring showed that BOD and COD effluent concentrations achieved quality targets in all facilities. As for the other pollutants, quality targets were met for most of the period. Operational costs of facilities bettered those set for the facility in the town of Baiyang and new village of Zhaojia, but exceeded them for the facility in the village of Dongbei. The main reasons for the differences were the electricity billing system and operational system for each facility. In order to promote small-scale aeration-based domestic wastewater treatment plants in rural China in the future, the issue of what constitutes efficient facility maintenance first needs to be addressed.