Fate of faecal pathogen indicators during faecal sludge composting with different bulking agents in tropical climate

Fecal sludge characterization, treatment, and resource recovery options: a state-of-the-art review on fecal sludge management

A rise in population and urbanization demanded that a robust fecal sludge management (FSM) value chain be used to restructure the sanitation system throughout the world securely. A significant global need exists to adopt efficient and sustainable FSM. On-site sanitation systems (OSS) produce fecal sludge (FS). FS is produced when excreta and blackwater are combined and stored or treated, either alone or in combination with greywater. FS can be semisolid or slurry and raw or partially digested. Critical examination of FS characteristics, i.e., biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids (TS), and pathogen count, varies from 600-56,836 mg/l, 6656 to 201,200 mg/l, 830-123,000 mg/l, and 105 to 109 E. coli/l of FS respectively. Helminth eggs range from 2500-25,000/l of FS. Public health and the environment are negatively impacted by septic tank overflows and the careless discharge of FS into open spaces affecting groundwater quality, water bodies, irrigation fields, open drains, places outside villages, etc. Thus, deciding on a proper treatment technology for FS before discharging it into open land or reusing FS is essential to create a pollution-free environment. This paper highlights the practices adopted for FSM under its different processes, such as collecting, characterization, treating, and reusing of on-site FS and bibliometric analysis on documents on fecal sludge. A thorough analysis has been carried out by reviewing all important literature available globally.

Effect of Turning Frequency on the Survival of Fecal Indicator Microorganisms during Aerobic Composting of Fecal Sludge with Sawdust

The study investigated the effect of turning frequency on survival of fecal indicator pathogens (E. coli, Enterococcus spp., Salmonella spp. and helminth eggs) during fecal sludge (FS) co-composting with sawdust. Dewatered FS was mixed with sawdust and composted on a pilot scale using different turning frequencies-i.e., 3 days (3TF), 7 days (7TF), and 14 days (14TF). Composting piles were monitored weekly for survival of fecal indicator microorganisms and evolution of selected physical and chemical characteristics for 14 weeks. Our results show that turning frequency has a statistically significant (p < 0.05) effect on pathogen inactivation in FS compost. The 3TF piles exhibited shorter pathogen inactivation periods (8 weeks) than 7TF and 14TF piles (10 weeks). Temperature-time was found to be the major factor responsible for the survival of pathogens in FS composting piles, followed by indigenous microbial activities and toxic by-products (monitored as NH₄⁺-N). Our study findings suggest that even at low composting temperatures, the high turning frequency can enhance pathogen inactivation. This is a significant finding for composting activities in some rural areas where suitable organic solid waste for co-composting with FS to attain the recommended high thermophilic conditions could be greatly lacking.

Technologies for pollutant removal and resource recovery from blackwater: a review

Blackwater (BW), consisting of feces, urine, flushing water and toilet paper, makes up an important portion of domestic wastewater. The improper disposal of BW may lead to environmental pollution and disease transmission, threatening the sustainable development of the world. Rich in nutrients and organic matter, BW could be treated for resource recovery and reuse through various approaches. Aimed at providing guidance for the future development of BW treatment and resource recovery, this paper presented a literature review of BWs produced in different countries and types of toilets, including their physiochemical characteristics, and current treatment and resource recovery strategies. The degradation and utilization of carbon (C), nitrogen (N) and phosphorus (P) within BW are underlined. The performance of different systems was classified and summarized. Among all the treating systems, biological and ecological systems have been long and widely applied for BW treatment, showing their universality and operability in nutrients and energy recovery, but they are either slow or ineffective in removal of some refractory pollutants. Novel processes, especially advanced oxidation processes (AOPs), are becoming increasingly extensively studied in BW treatment because of their high efficiency, especially for the removal of micropollutants and pathogens. This review could serve as an instructive guidance for the design and optimization of BW treatment technologies, aiming to help in the fulfilment of sustainable human excreta management.

Molecular transformation of dissolved organic matter and formation pathway of humic substances in dredged sludge under aerobic composting

Using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) and molecular reaction network analysis, this study investigated molecular transformation of dissolved organic matter (DOM) and formation pathway of humic substances (HS) in dredged sludge during aerobic composting. The results showed that macromolecular N-containing compounds in dredged sludge are abundantly transformed into unsaturated and aromatic oxygenated compounds, exhibiting physicochemical properties similar to those of humus. Especially, N-containing compounds with one nitrogen atom are susceptible to oxidative deamination. Furthermore, assemblages of reactive fragments (e.g., -C7H8O2, -C10H12O2, -C2H2O2, and -C4H6O2) were identified as potential precursors to HS formed by the following reactions: starting with protein deamination and desulfurization, lignin delignification cascaded, finally decarbonylation occurred. This work provides novel insight for optimizing the process of stabilization and humification of dredged sludge.

Recycling of Faecal Sludge: Nitrogen, Carbon and Organic Matter Transformation during Co-Composting of Faecal Sludge with Different Bulking Agents

This study investigated the effect of locally available bulking agents on the faecal sludge (FS) composting process and quality of the final FS compost. Dewatered FS was mixed with sawdust, coffee husk and brewery waste, and composted on a pilot scale. The evolution of physical and chemical characteristics of the composting materials was monitored weekly. Results indicate that bulking agents have a statistically significant effect (p < 0.0001) on the evolution of composting temperatures, pH, electrical conductivity, nitrogen forms, organic matter mineralisation, total organic carbon, maturity indices, quality of the final compost and composting periods during FS composting. Our results suggest reliable maturity indices for mature and stable FS compost. From the resource recovery perspective, this study suggests sawdust as a suitable bulking agent for co-composting with FS-as it significantly reduced the organic matter losses and nitrogen losses (to 2.2%), and improved the plant growth index, thus improving the agronomic values of the final compost as a soil conditioner. FS co-composting can be considered a sustainable and decentralised treatment option for FS and other organic wastes in the rural and peri-urban communities, especially, where there is a strong practice of reusing organic waste in agriculture.

Public health performance of sanitation technologies in Tamil Nadu, India: Initial perspectives based on E. coli release

Sanitation is intended to reduce the spread and burden of diseases transmitted from excreta. Pathogen reduction from excreta before sludge or effluent discharge to the environment would seem a logical and useful performance indicator for sanitation systems. However, the relative magnitudes of pathogen release from common sanitation technologies are not well understood. We, therefore, investigated the feasibility of performance measurement of different sanitation technologies in Tamil Nadu, India in reducing the release of the pathogen indicator Escherichia coli (E. coli). After conducting users’ surveys and technical assessments of the locally prevalent sanitation systems, we classified them into 7 distinct categories (based on both observed physical characteristic and usage) within a widely-accepted physical typology. Faecal sludge and wastewater samples were collected and analysed for E. coli and total solids from 136 household systems, 24 community systems, and 23 sanitary sewer oveflows. We estimated the average volumetric release rates of wastewater and faecal sludge from the different sanitation technologies. Average daily per capita E. coli release was computed, and used as one indicator of the public health performance of technologies. We found that on-site installations described by owners as “septic systems” included diverse forms of tanks and pits of uncertain performance. We observed a statistically significant difference in the average daily per capita E. coli release from different sanitation technologies (p = 0.00001). Pathogen release from the studied on-site sanitation technologies varied by as much as 5 orders of magnitude from “lined pits” (5.4 Log10 E. coli per person per day) to “overflowing sanitary sewers” and “direct discharge pipes” (10.3–10.5 Log10 E. coli per person per day). Other technologies lay between these extremes, and their performances in E. coli removal also varied significantly, in both statistical and practical terms. Our results suggest that although faecal sludge management along the sanitation service chain is important, sanitation planners of the observed systems (and probably elsewhere) should direct higher priority to proper management of the liquid effluents from these systems to minimize public health hazards. We conclude that (i) the work demonstrates a new and promising approach for estimating the public health performance of differing sanitation technologies, (ii) if E.coli is accepted as an indicator of the public health hazard of releases from sanitation systems, our results strongly suggest that safe containment of excreta for an extended period substantially reduces pathogen numbers and the risk of pathogen release into the environment; and (iii) there are some simple but little-used technical improvements to design and construction of on-site sanitation systems which could significantly reduce the release of pathogens to the environment.

"You need to dispose of them somewhere safe": Covid-19, masks, and the pit latrine in Malawi and South Africa

The ongoing Covid-19 pandemic has generated an immense amount of potentially infectious waste, primarily face masks, which require rapid and sanitary disposal in order to mitigate the spread of the disease. Yet, within Africa, large segments of the population lack access to reliable municipal solid waste management (SWM) services, both complicating the disposal of hazardous waste, and public health efforts. Drawing on extensive qualitative fieldwork, including 96 semi-structured interviews, across four different low-income communities in Blantyre, Malawi and Durban, South Africa, the purpose of this article is to respond to a qualitative gap on mask disposal behaviours, particularly from within low-income and African contexts. Specifically, our purpose was to understand what behaviours have arisen over the past year, across the two disparate national contexts, and how they have been influenced by individual risk perceptions, established traditional practice, state communication, and other media sources. Findings suggest that the wearing of cloth masks simplifies disposal, as cloth masks can (with washing) be reused continuously. However, in communities where disposable masks are more prevalent, primarily within Blantyre, the pit latrine had been adopted as the most common space for 'safe' disposal for a used mask. We argue that this is not a new behaviour, however, and that the pit latrine was already an essential part of many low-income households SWM systems, and that within the Global South, the pit latrine fulfils a valuable and uncounted solid waste management function, in addition to its sanitation role.

Open-air storage with and without composting as post-treatment methods to degrade pharmaceutical residues in anaerobically digested and dewatered sewage sludge

Over a period of 12 months, the fate of three hormones, 12 antibiotics and 30 pharmaceutically active substances (PhACs) was investigated during open-air storage without and with composting of anaerobically digested and dewatered sewage sludge. The effect of oxidation conditions during storage on degradation of hormones and PhACs in the sludge biomass was also examined. Under summer and winter conditions in Uppsala County, Sweden, two field-scale sludge windrows were constructed: open-air storage of sewage sludge windrow without composting (NO-COM)) and open-air storage windrow with composting (COM). NO-COM achieved effective removal of ∑Hormones (85%) and ∑Antibiotics (95%), but lower removal of ∑PhACs (34%), during the study year. The top layers of the sludge pile had significantly lower concentrations of ∑PhACs (3100-5100 ng/g ash) than deeper layers (8000-11,000 ng/g ash). After one year of composting, the degradation in the COM windrow resulted in concentrations of ∑Hormones (<LOD), ∑Antibiotics (<LOD), while the ∑PhCAs was 5% (730 ng/g ash) of initial (13,000 ng/g ash). The half-life of substances during composting in COM was within 7-100 days for all substances except ibuprofen (156 days). The first-order degradation constant (K) was the lowest for ibuprofen (0.0045 day^-1) and the highest for oxazepam (0.0805 day^-1). In conclusion, composting of sludge was effective in degrading the target hormones, antibiotics, and PhACs.

Toxicity and physicochemical parameters of composts including distinct residues from agribusiness and slaughterhouse sludge

Composting is useful for treatment of residues from agribusiness, but the potential toxicity of the final compost should be evaluated before its agricultural destination. The objective of this study was to evaluate the physicochemical characteristics and the toxicity of agribusiness residues using onion seeds as bioindicators. All tested treatments were composed by sludge from a swine slaughterhouse and sawdust. Besides the control, which included no additional materials, the other treatments included aviary bedding, rice husk and residue from tobacco industries as structuring materials. After 120 days of composting, for all treatments, the temperature inside the composting piles approached the environmental temperature, the physicochemical parameters indicated that the composts were stabilized and, except for the treatment including tobacco residues, that could be used for agriculture without impairing plant germination. Although the treatments including tobacco residues and rice husk showed evidence of cytotoxicity and genotoxicity at the beginning of the composting period, that was not observed for the treatment including aviary bedding. Such potential toxicity was not observed at the end of composting for any of the tested treatments.

Differences of Enzymatic Activity During Composting and Vermicomposting of Sewage Sludge Mixed With Straw Pellets

The study aims were focused on profiling eight hydrolytic enzymes by fluorescence method using a multifunctional modular reader and studying the proportion of basic microorganism groups during composting and vermicomposting of sewage sludge mixed with straw pellets in several proportions (0, 25, 50, 75, and 100%). The greatest decrease in enzymatic activity occurred in the first half of composting and vermicomposting. After 4 months of these processes, the least enzymatic activity was observed in the sludge with 50% and also 25% straw addition, indicating that straw is an important means for the rapid production of mature compost from sewage sludge. Enzymatic activity was usually less in the presence of earthworms than in the control treatment because some processes took place in the digestive tract of the earthworm. For the same reason, we observed reduced enzyme activity during fresh feedstock vermicomposting than precomposted material. The final vermicompost from fresh feedstocks exhibited less microbial biomass, and few fungi and G- bacteria compared to precomposted feedstock. The enzymatic activity during composting and vermicomposting of sewage sludge and their mixtures stabilized at the following values: β-D-glucosidase-50 μmol MUFG/h/g dw, acid phosphatase-200 μmol MUFP/h/g dw, arylsulphatase-10 μmol MUFS/h/g dw, lipase-1,000 μmol MUFY/h/g dw, chitinase-50 μmol MUFN/h/g dw, cellobiohydrolase-20 μmol MUFC/h/g dw, alanine aminopeptidase-50 μmol AMCA/h/g dw, and leucine aminopeptidase-50 μmol AMCL/h/g dw. At these and lesser values, these final products can be considered mature and stable.

Industrial Composting of Sewage Sludge: Study of the Bacteriome, Sanitation, and Antibiotic-Resistant Strains

Wastewater treatment generates a huge amount of sewage sludge, which is a source of environmental pollution. Among the alternatives for the management of this waste, industrial composting stands out as one of the most relevant. The objective of this study was to analyze the bacterial population linked to this process and to determine its effectiveness for the reduction, and even elimination, of microorganisms and pathogens present in these organic wastes. For this purpose, the bacteriome and the fecal bacteria contamination of samples from different sewage sludge industrial composting facilities were evaluated. In addition, fecal bacteria indicators and pathogens, such as Salmonella, were isolated from samples collected at key stages of the process and characterized for antibiotic resistance to macrolide, β-lactam, quinolone, and aminoglycoside families. 16S rRNA phylogeny data revealed that the process clearly evolved toward a prevalence of Firmicutes and Actinobacteria phyla, removing the fecal load. Moreover, antibiotic-resistant microorganisms present in the raw materials were reduced, since these were isolated only in the bio-oxidative phase. Therefore, industrial composting of sewage sludge results in a bio-safe final product suitable for use in a variety of applications.

A critical review on sludge management from onsite sanitation systems: A knowledge to be revised in the current situation

Access to safe excreta disposal is a basic human right and an essential element of human development. Developing countries (like India) have constructed millions of toilets with on-site sanitation technologies (OSTs). However, these OSTs lack the required management system for collection, transportation and disposal of Faecal Sludge (FS, sludge getting accumulated in OST), leading to considerable water and soil pollution. The major challenge in FS Management is the collation of scattered data and concentrated experiences (i.e., existing knowledge remains with the practitioners in the field without a written record). Therefore, a critical review of existing knowledge on OST, FS collection, transportation, and its utilisation is essential. This study highlighted shortcomings associated with existing OST, FS collection, transportation, and treatment systems. Furthermore, this study provided a framework for appropriate selection of OST based on available sanitation chains, and a critical analysis of FS characteristics (i.e., total solids, pH, electrical conductivity, biological oxygen demand, chemical oxygen demand, and pathogens of FS ranged from 830 to 72000 mg/L, 6.8 to 7.8, 1.9 to 3.5 mS/cm, 500-5000 mg/L, 100 to 49,000 mg/L, and 10⁶ to 10⁷ E-coli and 10³ to 10⁴ parasitic worms per litre of FS, respectively) to design treatment systems for FS utilisation as a resource in agricultural, aqua-culture, and construction application.

Composting of Olive Mill Pomace, Agro-Industrial Sewage Sludge and Other Residues: Process Monitoring and Agronomic Use of the Resulting Composts

The viability of co-composting of olive mill pomace added to sewage sludge with other organic residues was evaluated and the agronomic use of the final composts was investigated. Two composting piles at different carbon-nitrogen ratios were performed, in which olive mill pomace (OMP), sewage sludge from vegetable processing (SS), fresh residues from artichoke processing residues (AR), and wheat straw (WS) were used. The two composting piles were placed inside a specially built greenhouse and a turning machine pulled by a tractor was used for turning and shredding the organic matrix (every 6 days) during the process. The humidity and temperature of organic matrices have been monitored and controlled during the entire composting process, which lasted 90 days. The process was also monitored to evaluate the microbiological safety of the final compost. The humidity of both piles was always kept just above 50% until the end of the thermophilic phase and the maximum temperature was about 50 °C during the thermophilic phase. The carbon-nitrogen ratio decreased from 21.4 and 28.2, respectively (initial value at day 1 in Pile A and B), to values ranging from 12.9 to 15.1, both composts that originated from the two different piles were microbiologically safe. During a two-year period, the effects of different types of compost on the main qualitative parameters of processing tomato and durum wheat was evaluated. Five fertilization treatments were evaluated for tomato and durum wheat crops: unfertilized control (TR₁); compost A (TR₂); compost B (TR₃); ½ mineral and ½ compost A (TR₄); and mineral fertilizer commonly used for the two crops (TR₅). Concerning the processing tomato yield, TR₅ and TR₄ showed the best results (2.73 and 2.51 kg, respectively). The same trend was observed considering the marketable yield per plant. The only difference was related to the treatments that included the compost (2.32, 1.77, and 1.73 kg/plant for TR₄, TR₃, and TR₂, respectively). As regards the qualitative parameters of tomato, the highest average weight of the fruits was found in the TR₅, TR₄, and TR₃ treatments (respectively, 73.67 g, 70.34 g, and 68.10 g). For durum wheat, only the protein component was differentiated between treatments. Furthermore, wheat grain yield parameters generally increased by combined application of mineral fertilizer and compost.