**5. Social sustainability**

Social assessment based on indicators portrays a big picture of multidimensional issues and facilitate decision making. Many key aspects such as community management aspects, satisfaction and opinions of users, service quality, materials and personnel managements, etc. have to be profoundly analyzed before and after the establishment of WWTPs [45]. In this light, social indicators are rapidly becoming the preferred tools for policymakers and public communicators for disseminating the information on the advantages and disadvantages of the WWTPs [77]. However, societal indicators are generally difficult to quantify and often their meaning and relevance is based on the local stakeholders [78]. The data on social indicators for UASB+TF in this review is lacking since data availability on TF. This does not impair our comparison as it's combinations with other systems is a disadvantage identified at the global level in developing countries [79]. Hence, assessment of the chosen indicators is based on TF studied [43]. Caution should be exercised that all the data for social assessment do not represent any generic weighting. The chosen indicators for this assessment are (i) simplicity of the system (ii) esthetics, and (iii) public acceptance of the technology.

#### **5.1 System manageability**

System manageability includes ease of construction, complexity of O&M issues and professional skills required for the troubleshooting of the issues during the O&M of the WWTPs. Studies on the social sustainability of WWTPs in India demonstrated that the UASB+DHS system has fewer mechanical parts than TF. The simple configuration of UASB+DHS system makes it easy for construction and several intensive studies have followed up the ramifications of sponge designs for the easy packaging and enhanced efficiency [76]. For developing countries, simplicity of the system might be a key factor in the selection of the WWTP. Due to simple construction, there are few mechanical parts for O&M issues and UASB +DHS system has already been proven to be no laborious maintenance system [80]. Supplementary to this, the operators do not need to have a high technical knowledge.

#### **5.2 Esthetics**

UASB+DHS system has a slightly better stance on esthetics than the other TFs. Hydrogen sulphide (H2S) and ammonia (NH3) are the predominant objectionable *Downflow Hanging Sponge System: A Self-Sustaining Option for Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.94287*

odors in wastewater [81]. TF has been reported to have limited and passive aeration which might create an anaerobic condition which degrades organic matter and nutrients to release malodorous by-products. Also, TF is very sensitive to temperature change especially high temperatures which generate odors [5]. However, till this date, there are no evidences of odor problems in UASB+DHS system though it was operated at the high temperature in India (40°C). Nonetheless, both the systems have one common problem i.e. flies and snails which might affect the visual aethetics. Whilst none of the insects found have been found as a nuisance to the surrounding people and there is no evidences of any diseases caused by these insects. However, this issue could be resolved by the installation of nets or covers and cleaning with water sprays [82].

#### **5.3 Public acceptance of the technology**

One of the major problems faced during the establishment of WWTPs is its location. Very often resistance and protests from the local people significantly impact on the implementation of any social infrastructure plan [83, 84]. Therefore, "Public acceptance" is a key component when it comes to establishing a new WWTP [85]. In most of the researches, public acceptance of WWTPs facilities are based on concepts such as LULU (locally unwanted land use) and NIMBY (not in my backyard [86, 87]. These studies have highlighted the preferability of TF over activated sludge process. Besides, the result of investigation of Indian WWTPs has also exhibited that moderate value for the public acceptance of TF over UASB+DHS system and suggested WWTPs' location far from the settlement zones. Besides, the sludge and treated water from UASB+DHS system was used by the nearby farmers for agriculture and did not show any social concerns. It is clear that further studies need to be undertaken analyzing local conditions in a stepwise manner towards the acceptance of these technologies.

The above discussions on sustainability indicators assessment support the notion that DHS system could have a wide range of commercial applications for different kinds of wastewater. In most of the developing countries, centralized WWTP are limited to urban areas due to the several financial and social constraints. Likewise, many institutions such as large-scale apartments, complexes, hospitals, hotels, etc. need to maintain their own onsite WWTPs. Until now, the most preferred WWTP option was ASP based treatment plants. However, these systems are expensive due to its high operational and maintenance cost. On this verge, there is a potential use of DHS system as a substitute for ASP which would lead to huge commercial benefit. The technology validation of DHS system over ASP for developing countries has already been reported in several research investigations [12–18, 43]. Another area of commercial application of this system could be in aquaculture industry. Most of the aquariums and fish farms require frequent exchange of water leading to huge financial burden and increased workload. Current progressive researches on the application of DHS system for aquarium water treatment and live seafood transportation by minimizing the exchange of water and decreasing workload have broaden its scalability for aquaculture industry [21, 88]. In line with the environmental, economic and social sustainability of DHS system, it could have prospective applications in industrial wastewater treatment specifically for developing nations. Moreover, DHS reactor has commercial applications in the industries such as food processing industry, beverage industries, rubber processing industries and many agriculture products processing industries. Therefore, it could be concluded that with more researches and real scale implementation of this system, there could be a huge commercial demand for DHS system in near future.
