Table 2.

Potential of sludge recovery/utilization from wastewater.

No	Sludge Recovery/Utilization	Type of Wastewater	Summary of Findings	Country	Source
1	Algae biomass	Aquaculture	Chlorella sp. was recovered from aquaculture wastewater. The recovery process needs to be conducted with biodegradable coagulants in order to use the sludge further. Chitosan can perform 80% algae biomass recovery after coagulation–flocculation and sedimentation processes. Recovered biomass can be utilized as feed inside the biofloc cultivation pond system.	Malaysia	[39]
2	Algae biomass	Aquaculture	Derivates of Moringa oleifera showed potential to be used as bioflocculant to recover Chlorella sp. from aquaculture effluent. Biomass recovery efficiency using Moringa oleifera was significantly higher as compared to commercial chemical coagulant.	Malaysia	[145]
3	Nutrient into fertilizer	Domestic	Sludge of domestic wastewater contains high concentrations of nitrogen and phosphorus, which are essential nutrients for plant growth. Recovered sludge from domestic wastewater even contains trace elements, which might boost plant growth. Utilization of sludge from domestic wastewater needs to be accompanied by the utilization of biodegradable coagulants.	Eswatini	[143]
4	Nutrient into fertilizer	Domestic	Recovered domestic sewage sludge characterized as organic-rich solid may be very useful to provide readily bioavailable macro- and micro-components for plant growth. The result showed that the organic content in sludge can act as a soil conditioner.	Poland	[142]
5	Nutrients into fertilizer	Aquaculture	Recovered sludge from aquaculture effluent was used as biofertilizer for hot pepper plants. Positive effect on the plant height was obtained and considered to be comparable to that with the utilization of commercial fertilizer.	Nigeria	[146]
6	Nutrients into fertilizer	Domestic	Domestic wastewater contains high amounts of nutrients, which can be recovered as fertilizer. Recovered sludge as fertilizer has a characteristic of slow-release activity, which is useful for providing nutrients over a longer period of time.	Ohio	[137]